HER2-positive Early Breast Cancer Research Articles

Abstract PO2-01-05: Neoadjuvant pyrotinib plus trastuzumab, and chemoterapy in patients with HER2-positive early breast cancer: a real-world study

Abstract Background Pyrotinib is a new oral, irreversible pan-ErbB receptor tyrosine kinase inhibitor that targets human epidermal growth factor receptor 1 (HER1), HER2, and HER4. Previous studies have confirmed it combined with capecitabine is safe and well-tolerated in advanced breast cancer. And also PHEDRA trial had demonstrated the efficacy and safety of pyrotinib combined with trastuzumab and docetaxel neoadjuvant therapy early HER2-positive breast cancer. However, the efficacy of pyrotinib plus trastuzumab-based in real-world neoadjuvant therapy for early breast cancer is unknown. Purpose The present study aimed to explore the efficacy of pyrotinib-based in neoadjuvant therapy for early breast cancer in real-world. Method This is investigator-initiated phase 2 real-world study recruited eligible patients, aged 18–70 years with invasive carcinoma, cT2-3N0-3M0 stage, HER2-positive breast cancer. The patients received 400 mg pyrotinib orally once per day for 21 days and trastuzumab (8 mg/kg loading dose, 6 mg/kg maintenance dose) plus different standard chemotherapy, including six 21-day cycles of docetaxel (75 mg/m2) plus carboplatin (6 mg/mL/min), or four cycles of epirubicin (90 mg/m2) plus cyclophosphamide (600 mg/m2) and four cycles paclitaxel (80 mg/m2). The primary endpoint was to calculate the number of patients who achieved a pathological complete response (pCR, ypT0/is, ypN0). (ChiCTR2100052892). Result The results of the 23 patients were reported, The pCR of 12 (52.2%) patients, who reached the threshold for the design, was noted. The study is ongoing. The most frequent grade 3 to 4 adverse events were diarrhea (35.6%), which all the patients received primary prevention of diarrhea, leukopenia (44.8%), and anaemia (23.7%). However, no treatment-related deaths were recorded. Conclusion Previous studies have shown the efficacy and safety of pyrotinib plus trastuzumab and docetaxel in neoadjuvant therapy of HER2-positive early breast cancer. The current trial suggests that pyrotinib plus trastuzumab-based standard chemotherapy in real-world has promising efficacy and manageable toxicity in patients with HER2-positive early breast cancer in a neoadjuvant setting, the trial is ongoing, we will enroll more patients. Citation Format: Jun Zhou, Rui Wang. Neoadjuvant pyrotinib plus trastuzumab, and chemoterapy in patients with HER2-positive early breast cancer: a real-world study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-01-05.

Abstract PO2-01-07: Real-world efficacy of dual HER2-blockade in combination with anthracycline-containing and anthracycline-free neoadjuvant treatment in early breast cancer (BC)

Abstract BACKGROUND: Neoadjuvant therapy with antiHER-2 blockade is the standard of care for HER-2 positive early BC. The objective of this treatment is tumor downstaging to increase resectability and pathological complete response (pCR), a reliable surrogate endpoint for survival. Adding Trastuzumab (T) to chemotherapy resulted in an improvement in pCR, however, resistance to this agent is common and the incorporation of Pertuzumab (P) to the neoadjuvant scene demonstrated an increase in pCR in the Peony (39.3% vs 21.8%) and Neosphere trials (45.8% vs 29%). Across all studies, pCR is even higher in patients (pts) with negative hormonal receptor (HR) status (50%-63%) (3, 4). Tryphaena and Berenice found low rates of cardiotoxicity with T-P combination. Recently, TRAIN-2 data showed that anthracyclines and platinum have a similar pCR (67% vs 68%), but febrile neutropenia and cardiotoxicity is higher in the anthracycline group, concluding that omitting this therapy might be a preferred approach in the presence of dual HER2 blockade. Our study investigated the pCR benefit of dual HER2 blockade with anthracyclines and platinum in HER2 positive early BC. METHODS: We conducted a retrospective, unicenter, observational study of pts, treated with neoadjuvant T-P plus chemotherapy, in HER-2 positive early BC, between April 2015 and December 2022 at University Hospital A Coruña (Spain). The primary endpoint was total pCR in breast and axila (tpCR: ypT0/is ypN0). Secondary endpoints were: association between clinicopatological characteristics and pCR; and between cardiotoxicity and treatment pattern. Statistical analyses were conducted with Statistical Package for the Social Science (SPSS). RESULTS: During the study period, from April 2015 to May 2022, 154 pts were enrrolled. The median age was 51,3 years [range 26 – 799 years], all patients were female. Infiltrating ductal carcinoma was present in 92.2% pts, and 5.8% were inflammatory BC. At diagnosis, 11.7%, 61.7% and 26.6% had stages I, II and III, respectively, and 51.3% revealed axillary node involvement. Among observed cases, 94 (61%) were positive HR; 68 (45%) had histological grade 2 and 83 (53.9%) histological grade 3 tumors; and 151 pts (99.3%) presented a ki-67 level >20%. HER2 by immunohistochemistry (IHC) resulted in 3+ for 133 pts (86.9%) and in 2+ for 20 pts (13.1%), all of them with positive result by in situ hybridation (ISH). P-T were mostly combined with anthracyclines (64.9%). tpCR rate was 50.6%, and it was not significantly different according chemotherapy approach. tpCR was significantly higher among HR negative tumours (73.3%) compared with HR positive (36.2%) (p= 0.001), and in HER2 positive 3+ (55.6%) compared with HER2 positive 2+ (15%) tumours (p= 0.001). Achievement of tpCR was not significantly associated with tumor size, stage, histological grade and ki-67 level. Breast pCR was higher than tpCR (54.2%). 13 pts (8.4%) presented recurrence disease, in 76.9% of cases was a metastatic relapse. Cardiotoxicity was low during all stages of treatment and was not significantly associated with chemotherapy pattern. CONCLUSIONS: Neoadjuvant T-P plus chemotherapy with either anthracyclines or platinum therapy, demonstrated same efficacy and cardiac safety in our real-world study. pCR rates are lower in positive HR and HER2 positive 2+, needing more investigation with combination strategies including hormonotherapy, Our results are similar to data from randomized trials and other real-world efficacy studies, but we need more follow-up to identify late cardiotoxicity by anthracyclines and recurrences in positive HR tumors. Citation Format: Beatriz Alonso de Castro, Cristina Reboredo, Lourdes Calvo, Maria-Eva Perez-Lopez, Martin Igor Gomez Randulfe Rodriguez, Sofia silva diaz, Iria Parajo Vazquez, Silvia Antolin Novoa. Real-world efficacy of dual HER2-blockade in combination with anthracycline-containing and anthracycline-free neoadjuvant treatment in early breast cancer (BC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-01-07.

Abstract GS03-12: Phase III study of adjuvant ado-trastuzumab emtansine vs trastuzumab for residual invasive HER2-positive early breast cancer after neoadjuvant chemotherapy and HER2-targeted therapy: KATHERINE final IDFS and updated OS analysis

Abstract Background: Patients with HER2-positive early breast cancer (EBC) who have residual invasive disease after neoadjuvant chemotherapy + HER2-targeted therapy have a high risk of recurrence and death. The standard of care when KATHERINE was designed was continuation of the same HER2-targeted therapy in the adjuvant setting for 1 year. The primary analysis of KATHERINE in 2018 showed that the risk of recurrence of invasive BC or death was 50% lower with adjuvant ado-trastuzumab emtansine (T-DM1) than with trastuzumab. Methods: KATHERINE (NCT01772472/BO27938/NSABP B-50-I/GBG 77) is a phase III, open-label, global study of patients with centrally confirmed, HER2-positive (immunohistochemistry 3+ or in situ hybridization-positive) primary BC (T1–4, N0–3, M0) who received neoadjuvant chemotherapy + HER2-targeted therapy, which had to include a taxane and trastuzumab, followed by surgery, with pathologically documented residual invasive disease in the breast and/or axillary lymph nodes. Within 12 weeks of surgery, patients were randomized 1:1 to T-DM1 (3.6 mg/kg intravenously [IV] every 3 weeks [q3w]) or trastuzumab (6 mg/kg IV q3w) for 14 cycles. Randomization was stratified by clinical stage at presentation, hormone receptor status, single vs dual neoadjuvant HER2-targeted therapy, and pathologic nodal status after neoadjuvant therapy. Patients received radiotherapy and/or endocrine therapy per local standards. The primary endpoint was invasive disease-free survival (IDFS). We report the final IDFS analysis, which was to occur after ~384 events had been reported, and the preplanned second interim analysis of overall survival (OS); specified to occur at the same time. Results: With a median follow-up of 8.4 years (101 months), T-DM1 sustained the improvement in IDFS over trastuzumab (unstratified hazard ratio [HR] 0.54; 95% confidence interval [CI] = 0.44, 0.66; p < 0.0001). Landmark 7-year IDFS rates were increased from 67.1% with trastuzumab to 80.8% with T-DM1; a difference of 13.7%. At clinical cutoff for the final IDFS analysis, 215 deaths had been reported. T-DM1 significantly reduced the risk of death by 34% compared with trastuzumab (unstratified HR 0.66; 95% CI = 0.51, 0.87; p = 0.0027). Deaths had occurred in 89/743 patients (12.0%) in the T-DM1 arm and 126/743 (17.0%) in the trastuzumab arm. Landmark 7-year OS rates were increased from 84.4% with trastuzumab to 89.1% with T-DM1; a difference of 4.7%. OS and IDFS benefits were seen across key subgroups. A low incidence of adverse events (AEs) related to study treatment or to study procedures was observed during the post-treatment period: Grade ≥3 related AEs occurred in 3/740 patients (0.4%) in the T-DM1 arm and 3/720 (0.4%) in the trastuzumab arm; serious related AEs, in 2/740 (0.3%) and 4/720 (0.6%), respectively. Related AEs classed as “cardiac disorders” were rare in both arms with extended follow-up. Conclusions: After 8.4 years (101 months) median follow-up, T-DM1 significantly improved OS in patients with HER2-positive EBC with residual invasive disease after neoadjuvant therapy. The IDFS benefit of T-DM1 was sustained in the intention-to-treat population with longer follow-up, and no new safety issues emerged. Cardiac toxicity was rare in both arms. T-DM1 is the first therapy to show improved survival post-surgery in patients with HER2-positive EBC with residual invasive disease after neoadjuvant therapy. Follow-up is ongoing for the final OS analysis. Citation Format: Sibylle Loibl, Max Mano, Michael Untch, Chiun-Shen Huang, Eleftherios Mamounas, Norman Wolmark, Adam Knott, Asna Siddiqui, Thomas Boulet, Beatrice Nyawira, Eleonora Restuccia, Charles Geyer. Phase III study of adjuvant ado-trastuzumab emtansine vs trastuzumab for residual invasive HER2-positive early breast cancer after neoadjuvant chemotherapy and HER2-targeted therapy: KATHERINE final IDFS and updated OS analysis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS03-12.

Abstract PO4-01-06: HER2-positive early breast cancer (EBC): treatment, toxicities and outcomes in a retrospective cohort of elderly patients (pts)

Abstract Background: Approximately one-third of breast cancer cases are diagnosed in women aged ≥70 years, presenting a considerable challenge to offer optimal treatment options. Ensuring appropriate care involves taking into account factors such as geriatric evaluation, comorbidities, and life expectancy. However, the lack of literature focusing on the elderly population makes it difficult to choose the correct treatment approach. Methods: We conducted a retrospective analysis including all elderly pts (≥70 years) with HER2-positive EBC treated at Vall d’Hebron hospital between 2016-2022. We evaluated treatment schemes, toxicities, and outcomes. Disease-free survival and overall survival from the time of diagnosis were assessed using Kaplan-Meier estimates. Results: Among 118 pts identified, the median age of diagnosis was 79.5 years (74-85). The main comorbidities were cardiovascular (82.2%), diabetes (19.5%), pulmonary (10.2%), and kidney diseases (9.3%). Stages (s) at diagnosis were: 16.8% sI, 56% sII and 24.8% sIII. 64.8% were hormone receptor-positive, 78.4% were HER2 3+ and 15.2% 2+ (ISH amplified). Median follow up was 29.1 months (m). Neoadjuvant (NA) treatment was administered to 60.2% of pts (n=71) of which 74.6% (n=53) received chemotherapy (CT) with taxanes (Tax) only (72.5%), anthracyclines (Ac)+Tax (17.6%) and Tax+carboplatin (7.8%). AntiHER2-agents were administered in 80.3% pts (n=57) of which 89.1% received trastuzumab and pertuzumab. 23.9% of pts (n=17) received exclusively aromatase inhibitor and 2.8% (n=2) associated double blockade. Overall, 87.3% (n=103) and 80% of NA treated pts (n=57) underwent surgery, specifically mastectomy in 37.9% and 46,6% pts in the NA group achieved a pathological complete response (pCR). 38.9% pts (n=46) were treated with surgery upfront. Adjuvant treatment (A) was administered to 82.9% (n=97) of pts, with 23.7% (n=23) receiving CT; primarily Tax (82.6%), Ac+Tax (13%) and Tax+carboplatin (4.3%). AntiHER2-agents were administered in 87.6% of pts (n=85). In the overall population, median disease-free survival (mDFS) and median overall survival (mOS) were 81.1m (95% CI 68.7-not reached [NR]) and 81.1m (95% CI 77.4-NR) respectively. In the pts who underwent surgery, mDFS was 81.1m (95% CI 68.7-NR), whereas mDFS in those who did not, was 17.6m (95% CI 13.1-NA). Pts who received antiHER2-agents in the A setting showed a mDFS of 81.1m (95% CI 81.1-NR) and mOS was NR (95% CI 81.1-NR) compared to those who did not, with a mDFS of 39.7m (95% CI 25.4-NR) and mOS of 77.4m (95% CI 25.4-NR). Toxicities were reported in 78.3% of pts (n=54) receiving NA treatment and in 54.7% of pts (n=52) in the A setting of which 25.9% (n=14) and 13.4% (n=7) corresponded to grade (G) 3 respectively. Hospitalization, treatment discontinuation and dose reduction were required in 13%, 25.9% and 29.6% of pts with NA treatment and in 23.1% and 19.6% of A pts respectively with no pts requiring hospitalization. NA/A main side effects included asthenia 70.4% (nG3=2)/67.3% (nG3=2), diarrhea 64.8% (nG3=4)/19.2% (no≥G3), neuropathy 27.8% (no ≥G3)/28.8% (nG3=1), nausea/vomiting 22.2%/3.9% (no ≥G3), infusion reaction 20.4% (nG3=2)/5.9% (no ≥G3) and cardiotoxicity in 3.8% (nG3=1)/7.8% (nG3=2). Conclusions: Our study provides real world data about the use of tailored treatments to reach a balance between treatment response and tolerance in an elderly population, with low discontinuation rates, satisfactory pCR rates and long-term results in patients treated with antiHER2-agents. It is crucial to evaluate risks and benefits of treatments in frail patients. Therefore, an oncogeriatric assessment program was started in 2021 to prospectively perform dedicated research in this population. Citation Format: Alejandra Rezqallah, Diego Gómez-Puerto, Ridhi Ranchor, Laia Joval-Ramentol, Lucia Sanz, Maria Borrell, Marcelo Alvarado-Cárdenas, Antonio San-José, Clara Morales Comas, Martin Espinosa-Bravo, Manuel Altabas, Esther Zamora, Carolina Ortiz, Patricia Gómez Pardo, Isabel Pimentel, Meritxell Bellet- Ezquerra, Mafalda Oliveira, Cristina Saura, Míriam Arumí, Santiago Escrivá-de-Romaní. HER2-positive early breast cancer (EBC): treatment, toxicities and outcomes in a retrospective cohort of elderly patients (pts) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-01-06.

Abstract PO5-19-01: The HER2-RADiCAL study (Response ADaptive CAre pLan) – Tailoring treatment for HER2 positive early breast cancer

Abstract Background The presence or absence of residual disease following neoadjuvant systemic anti-cancer therapy (neoSACT) for HER2-positive early breast cancer (HER2+ EBC) provides powerful prognostic information. Pathological complete response (pCR) following neoSACT, particularly in patients with earlier clinical TNM stage at diagnosis, identifies a population with excellent survival outcomes in whom the balance of toxicity associated with the current treatment pathway may be disproportionate to absolute clinical benefit. Aims >HER2-RADiCAL seeks to reduce the treatment burden and healthcare costs of treating HER2+ EBC by testing the hypothesis that pCR can be used as a functional response biomarker to select patients who can safely receive less systemic therapy with minimal/no loss of efficacy. Trial design and eligibility criteria HER2-RADiCAL is a response-directed interventional cohort/threshold-crossing design study embedded within a real-world data-driven clinical pathway model. Patients with ER-positive or negative HER2+ EBC with cT1N1 or cT2N0-1 stage at diagnosis are eligible after completion of standard of care neoSACT and locally determined pCR (ypT0/Tis ypN0). Patients with pathological features consistent with previous malignant involvement in >4 nodes are not eligible. Adjuvant trastuzumab +/- pertuzumab may have continued prior to study entry provided no more than 9 cycles of trastuzumab are received. After registration all participants receive a total of 9 cycles of trastuzumab including those administered prior to study entry. Participants receive no further pertuzumab and no adjuvant chemotherapy. Adjuvant endocrine therapy and radiotherapy are given as per standard of care. Central pathology review of pCR status will be conducted in a subset of cases. A Study Within a Trial (SWAT) will explore identification of factors influencing patient decision-making for participation in studies of response-adapted treatment. Statistical methods The primary endpoint is relapse-free interval. Recruitment of 720 participants over 3.5 years will provide 90% power to exclude an event rate >6.5% at 3 years (expected event rate ≤4%). Secondary endpoints include relapse-free survival, invasive breast cancer-free survival, invasive disease-free survival, distant recurrence-free interval, breast cancer-free interval, overall survival, treatment pathway adherence and cost-effectiveness. An interventional cohort is preferred to a randomised non-inferiority trial based on the known event rate in this population which is sufficiently low such that any deviation from this expected event rate would indicate failure of the reduced therapy strategy. Real-world data driven clinical pathway model Health economic modelling will compare the protocol-driven study cohort with two comparator pathways: a non-response adapted maximum therapy pathway (the standard clinical pathway prior to the study) and a real-world representative pathway derived from anonymised data for all patients treated for HER2+ EBC within the UK NHS. Patient and public involvement Our PPI partners continue to shape this research, holding key roles as trial management group members, overseeing progress of the study, contributing to protocol amendment development, and design and implementation of the SWAT. Current status The first patient was enrolled in December 2021. At 10th July 2023, 25 research sites have opened with 39 participants recruited. Site opening continues with a minimum target of 40. Responding to continued use of anthracycline-based regimens in UK practice, eligibility criteria have recently been extended to permit entry of patients who have received anthracycline-containing neoSACT. For further information contact her2radical-icrctsu@icr.ac.uk. Citation Format: Iain Macpherson, Stuart McIntosh, Lucy Kilburn, Holly Tovey, Laura Moretti, Katie Goddard, Indrani Bhattacharya, Clinton Boyd, Cliona Kirwan, Ciara O'Brien, Duncan Wheatley, Jennifer Glendenning, Mairead MacKenzie, Hilary Stobart, Claire Snowdon, Andrew Wardley, Abeer Shaaban, Peter Hall, David Cameron, Judith Bliss. The HER2-RADiCAL study (Response ADaptive CAre pLan) – Tailoring treatment for HER2 positive early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-19-01.

Abstract PO3-17-08: SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU

Abstract BACKGROUND: About 15% to 20% of breast cancers express positivity for human epidermal growth factor receptor 2 (HER2), a more aggressive breast cancer subtype with shorter survival. Trastuzumab, a humanized monoclonal antibody was approved by the U.S. Food and Drug Administration (FDA) for therapeutic use in metastatic breast cancer in 1998 and HER2-positive early breast cancer in 2006. HER2 overexpression is associated with more aggressive tumor growth and worse prognosis compared to HER2-negative tumors. HER2-positive tumors occur more frequently in younger women and node-positive women and are often less responsive to cytotoxic therapies. The primary objective of this study was to evaluate the tolerability of the subcutaneous formulation of trastuzumab in real life at the national institute of neoplastic diseases LIMA-PERU in patients with epidermal growth factor receptor 2 (HER2)-positive early breast cancer; efficacy was a secondary objective. METHOD: Female patients aged 18 years or older diagnosed between 2018-2019 with early epidermal growth factor receptor 2 (HER2)-positive breast cancer who received at least 1 dose of trastuzumab subcutaneously in a neo/adjuvant setting with or without chemotherapy were included. The treatment indication is 600 mg at a fixed dose every 3 weeks for 18 cycles. RESULTS: A total of 70 patients who received treatment with subcutaneous trastuzumab were included in the analysis. The mean age of the population was 52.6 ± 12.4 years, with the majority of patients being older than 50 years (54.29%). The mean number of subcutaneous trastuzumab cycles received was 11.4 ± 4.2. Adverse effects such as arthralgia (47.62%), diarrhea (9.52%), fatigue (9.52%) and injection site reaction (9.52%) occurred in 30% of patients. The mean number of cycles received until the first occurrence of adverse effects was 5.2 ± 2.1. It was observed that 97.14% completed treatment with trastuzumab subcutaneously, and 2.86% had to discontinue treatment. Cardiotoxicity and hypertension were the reasons why patients discontinued treatment. Of the patients included in the study, 63.77% received subcutaneous trastuzumab in the neoadjuvant setting, while the remaining 36.23% received it in the adjuvant setting. Of the patients, 45.71% started treatment with trastuzumab intravenously and received an average of 6 ± 3 cycles before switching to the subcutaneous presentation. After 3 years of follow-up, 7.14% developed disease progression; 57.1% had progression at the cerebral level, 28.6% at the local level and 14.3% at the pulmonary/hepatic level. 98.57% of patients are alive. CONCLUSIONS: In a real-life setting, subcutaneous trastuzumab is a well-tolerated and effective treatment option for patients even in patients who started treatment with the intravenous presentation and made the switch during treatment. Table 1: General clinical characteristics of patients XX XX Citation Format: Iris Otoya, Natalia Valdivieso, Zaida Morante, Carlos Castañeda, Silvia Neciosup, Mónica Calderón, Henry Gómez. SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-17-08.

Abstract PO1-01-02: Final analysis of neoadjuvant chemotherapy with pegylated liposomal doxorubicin/cyclophosphamide followed by taxanes with full-course trastuzumab/pertuzumab for HER2-positive breast cancer: a single-arm, phase II study

Abstract Background: The optimal neoadjuvant treatment regimen for HER2-positive breast cancer remains unclear, especially regarding the use of anthracycline. We conducted a prospective phase II study to evaluate sequential neoadjuvant chemotherapy with pegylated liposomal doxorubicin (PLD)/cyclophosphamide followed by taxanes in the presence of full-course trastuzumab/pertuzumab in HER2-positive early breast cancer patients. Methods: In this single-arm, open-label, multicenter, phase II study, eligible patients with confirmed HER2-positive early breast cancer were recruited from four independent hospitals. Patients received four cycles of PLD (35 mg/m2) and cyclophosphamide (600 mg/m2), followed by four cycles of taxanes (docetaxel, 100 mg/m2 or nab-paclitaxel, 260 mg/m2), concomitant with eight cycles of trastuzumab (8 mg/kg loading dose, then 6 mg/kg) and pertuzumab (840 mg loading dose, then 420 mg) every 3 weeks. The primary endpoint was total pathological complete response (ypT0/is ypN0, tpCR). Secondary endpoints included breast pCR (bpCR), objective response rate (ORR), disease control rate, the proportion of patients requiring breast-conserving surgery, and safety. For biomarkers analysis, tumor tissues were collected at baseline and evaluated for Topoisomerase 2 Alpha (TOP2A) expression assessed prospectively with immunohistochemistry (IHC) assay by independent pathologists. Results: Between May 27, 2020 and May 11, 2022, 78 eligible patients were treated and underwent surgery, of whom 42 (53.8%) patients underwent breast-conserving surgery. After neoadjuvant therapy, 47 (60.3%, 95% CI, 48.5%-71.2%) patients achieved a tpCR in the breast and axilla. The bpCR was observed in 49 (62.8%) patients. ORRs were 76.9% (95% CI, 66.0%-85.7%) and 93.6% (95% CI, 85.7%-97.9%) after 4-cycle and 8-cycle neoadjuvant therapy, respectively. All (100%) patients achieved disease control since the end of the first cycle. No correlations between clinicopathological variables and pathological response were observed. Grade 3 or worse AEs occurred in 35 (44.9%) patients. Nine (11.5%) patients experienced asymptomatic LVEF reduction (≥10% from baseline), but all with a minimum value of >55%. No treatment-related surgical delay or death occurred. For biomarkers analysis, the status of TOP2A was not found to be associated with pCR or 4th-cycle ORR. Conclusions: This dual HER2-blockade plus polychemotherapy as sequential neoadjuvant regimen demonstrates promising anti-tumor activity and acceptable tolerability for patients with HER2-positive breast cancer. Citation Format: Yaping Yang, Liang Jin, Yudong li, Fengxia Gan, Nanyan Rao, Jun Zhang, Ruifa Feng, Zhenzhen Liu, Qiang Liu. Final analysis of neoadjuvant chemotherapy with pegylated liposomal doxorubicin/cyclophosphamide followed by taxanes with full-course trastuzumab/pertuzumab for HER2-positive breast cancer: a single-arm, phase II study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-02.

Abstract PO3-15-01: Overexpression of N-glycosylation related gene OST4 promotes chemotherapy resistance in triple-negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, with high malignancy and poor outcome. Resistance to chemotherapy leads to treatment failure. How to overcome drug resistance is the key point in TNBC treatment. Previously, we initiated a prospective multicenter single-arm NeoPath clinical study (ClinicalTrial.gov identifier: NCT03907800) to assess the efficacy and safety of nab-paclitaxel combined with carboplatin in the neoadjuvant therapy of triple negative and HER2-positive early breast cancer. A total of 99 TNBC patients were enrolled and the pCR rate in TNBC was 33.78%. Samples before and after treatment were collected. RNA-sequencing results showed that OST4 was of high-expression in drug-resistant TNBC tumor tissues compared with chemo-sensitive samples. To verify the clinical significance of OST4 expression levels in TNBC, we tested the expression of OST4 by immunohistochemical technique on a tissue microarray including 87 TNBC cases treated with chemotherapy. We found that high expression of OST4 was associated with poor tumor differentiation, and patients with high OST4 expression had more relapse after chemotherapy. Ex-vivo proliferation assay and foci formation assay further confirmed that over-expression of OST4 promoted chemo-resistance, whereas down-regulating OST4 could reverse resistance in TNBC cell lines. As an oligosaccharyltransferase, it is reported that OST4 played parts in N-glycosylation. So we try to elucidate the relationship between N-glycosylation and drug resistance. Glycoproteomics results verified the existence of differential N-glycosylation atlas in drug-resistant tumor tissues compared with drug sensitive samples. NGS1 was identified as a potential target of OST4 by co-immunoprecipitation and mass spectrometry. In conclusion, high expression of OST4 could promote chemotherapy resistance in TNBC trough N-glycosylation regulation. Targeting OST4 may help reverse drug-resistance and improve therapeutic effect in TNBC. Citation Format: Wei Wang, Deyue Liu, Shuning Ding, Yan Fang, Jiayi Wu, Li Zhu. Overexpression of N-glycosylation related gene OST4 promotes chemotherapy resistance in triple-negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-15-01.

Abstract PS09-04: The benefit of adjuvant pertuzumab and trastuzumab according to estrogen receptor and HER2 expression: sub-analysis of the APHINITY trial

Abstract Background: Some studies suggest that response to HER2-targeting agents may differ according to estrogen receptor (ER) and HER2 expression levels. This study aimed to investigate the magnitude of benefit from the addition of pertuzumab to trastuzumab and chemotherapy according to ER and HER2 expression levels in the APHINITY trial. Methods: APHINITY (NCT01358877; BIG 4-11) was a randomized, double-blind, phase III study comparing the addition of pertuzumab or placebo to adjuvant trastuzumab and chemotherapy in an ITT population of 4804 patients with HER2-positive early breast cancer. The primary objective of this exploratory, unplanned analysis was to compare whether the addition of pertuzumab to trastuzumab had an impact in invasive disease-free survival (IDFS) within different subgroups defined by HER2 FISH amplification ratio and/or ER percentage of positivity on immunohistochemistry (IHC) (centrally assessed). Patients with a FISH ratio less than 2 were excluded from this analysis, leaving 4782 patients. IDFS was defined as the time from randomization until the date of the first occurrence of an IDFS event. HER2 FISH amplification ratio was categorized as low (2≤ FISH ratio < 5) vs. high (FISH ratio ≥5). ER expression on IHC was categorized as negative ( < 1%) vs. positive (≥1%). A subgroup analysis using Cox proportional hazards regression models was used to model IDFS, assessing four categories formed by cross classifying the FISH ratio and ER groups. The model was adjusted for randomized arm, adjuvant chemotherapy regimen received, and a combined variable of nodal status and protocol version. Results: The 4782 patients had a median age of 51 years old (IQR 44-59), with a median follow up time of 73.6 months (IQR 63.0-75.2). Most patients received an anthracycline-based chemotherapy (n=3712, 77.6%). ER expression was positive in 3047 patients (63.7%). HER2 FISH amplification ratio was high in 2479 patients (51.8%). All FISH ratio/ER subgroups seem to derive IDFS benefit from the addition of pertuzumab (HR < 1) (Table 1). The HER2 FISH ratio-low/ER positive subgroup had the largest reduction in risk of an IDFS event, 30% for the pertuzumab arm (HR=0.70, 95% CI 0.51-0.95) versus placebo. Smaller differences in IDFS events were observed between the treatment arms in the other subgroups. The subgroup of tumors with HER2 FISH ratio-high/ER-negative expression showed the numerically smallest benefit in IDFS events with the addition of pertuzumab (HR 0.85, 95% CI 0.59-1.25), see Table 1. Conclusions: In this APHINITY sub-analysis, patients treated with pertuzumab/trastuzumab derive similar benefit regardless of ER and HER2 expression levels. More research is needed to find predictive biomarkers to escalate or de-escalate treatments. Table 1. Abbreviations: FISH: fluorescence in situ hybridization, ER: estrogen receptor; IDFS: invasive disease-free survival; CI: confidence interval; HR: hazard ratio Citation Format: Evandro de Azambuja, Elisa Agostinetto, Faye Samy, Serena Di Cosimo, Philippe Aftimos, Noam Pondé, Daniel Eiger, Matteo Lambertini, David Cameron, Astrid Kiermaier, Andrew Bailey, Giuseppe Viale, Sherene Loi, Martine Piccart. The benefit of adjuvant pertuzumab and trastuzumab according to estrogen receptor and HER2 expression: sub-analysis of the APHINITY trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS09-04.

Abstract PO3-20-01: ASTEFANIA: a Phase III study of ado-trastuzumab emtansine plus atezolizumab or placebo as adjuvant therapy in patients with residual invasive breast cancer after neoadjuvant HER2-targeted therapy and chemotherapy

Abstract BACKGROUND Ado-trastuzumab emtansine (T-DM1) is the standard of care for adjuvant treatment of patients (pts) with HER2-positive early breast cancer (eBC) who have invasive residual disease after preoperative treatment with taxane and HER2-targeted therapy. However, a high unmet need remains in some higher risk subgroups (e.g., inoperable or lymph node-positive, hormone receptor-negative disease) who have 3-year invasive disease-free survival (IDFS) rates of 76%. Exploratory analyses suggest that addition of the programmed death-ligand 1 (PD-L1) inhibitor atezolizumab to T-DM1 results in longer progression-free survival compared with T-DM1 alone in pts with previously treated PD-L1-positive metastatic BC. PD-L1/programmed death-1 inhibitors may have a different effect in eBC, as they result in improved pathologic complete response in early triple-negative BC regardless of PD-L1 status. ASTEFANIA evaluates atezolizumab plus T-DM1 in PD-L1-unselected pts with higher risk residual invasive breast cancer after neoadjuvant treatment. TRIAL DESIGN ASTEFANIA is a Phase III, randomized, double-blind, multicenter, study in pts with centrally confirmed HER2-positive eBC with residual invasive disease at surgery after neoadjuvant chemotherapy and HER2-directed treatment including ≥9 weeks of taxane and ≥9 weeks of trastuzumab. Within 12 weeks of primary surgery, pts are randomized 1:1 to intravenous (IV) T-DM1 3.6 mg/kg every 3 weeks (q3w) plus atezolizumab 1200 mg IV q3w or T-DM1 3.6 mg/kg IV q3w plus placebo IV q3w for 14 cycles. Radiotherapy and/or endocrine therapy is administered per local standards. Randomization is stratified by clinical stage at presentation, hormone receptor status, preoperative HER2-directed therapy, and PD-L1 status. ELIGIBILITY CRITERIA Eligible pts have clinical stage cT4/any N/M0, any cT/N2–3/M0, or cT1–3/N0–1/M0 at presentation. Those with cT1–3/N0–1 disease must have pathologic evidence of residual invasive carcinoma in axillary lymph node(s) at surgery. Pts with cT1mi/T1a/T1b/N0 disease are not eligible. AIMS The primary endpoint is IDFS. Secondary endpoints include overall survival, safety, and patient-reported outcomes. STATISTICAL METHODS The log-rank test will be used to compare IDFS between the treatment arms, according to the protocol-defined stratification factors. The Cox proportional hazards model, stratified by the protocol-defined stratification factors, will be used to estimate the hazard ratio between the two treatment arms and its 95% confidence intervals. ACCRUAL As of Jun 28, 2023, 789 pts of the target of 1,700 have been enrolled. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT04873362. Originally presented at the ESMO Congress 2021, 202TiP, Peter Schmid et al. – Reused with permission. Further information is available in Future Oncology 2022; 18:3563–3572. Submitted with permission from Future Medicine & Future Science, part of the Future Science Group. Citation Format: Peter Schmid, Thomas Bachelot, Giampaolo Bianchini, Nadia Harbeck, Sherene Loi, Yeon Park, Aleix Prat, Leslie Gilham, Thomas Boulet, Nino Gochitashvili, Estefania Monturus, Chiara Lambertini, Beatrice Nyawira, Adam Knott, Sara Hurvitz. ASTEFANIA: a Phase III study of ado-trastuzumab emtansine plus atezolizumab or placebo as adjuvant therapy in patients with residual invasive breast cancer after neoadjuvant HER2-targeted therapy and chemotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-20-01.

Abstract PO1-27-05: De-escalated neoadjuvant weekly nab-paclitaxel with trastuzumab and pertuzumab in HER2-positive early breast cancer (HELEN-006):a randomized,phase 3 trial

Abstract Background: Chemotherapy de-escalation is currently under investigation as a treatment approach for HER2-positive early-stage breast cancer(EBC). We conducted a phase 3 clinical trial to evaluate the effectiveness of a weekly regimen of nab-paclitaxel monotherapy in combination with dual HER2 blockade for HER2-positive EBC. Methods: We conducted a multicenter, randomized, open-label Phase 3 trial at six hospitals in China. Eligible participants were women aged 18-70 with locally confirmed, HER2-positive, stage II-III, invasive, operable breast cancer and an Eastern Cooperative Oncology Group performance status of 0 or 1. Participants were randomly assigned (1:1) using central block randomization, with block sizes of four, stratified by hormone receptor status, tumor stage, and node status. They were assigned to receive either intravenous nab-paclitaxel (125mg/m2 on days 1, 8, and 15) for six 3-week cycles (group A), or intravenous docetaxel (75mg/m² on day 1) and carboplatin (area under the concentration-time curve 6mg/mL per min on day 1) for six 3-week cycles (group B). Both groups received concurrent trastuzumab (8mg/m2 loading dose, 6mg/m2 maintenance dose on day 1) and pertuzumab (intravenous 840mg loading dose, 420mg maintenance dose on day 1). The primary endpoint was the proportion of patients achieving a pathological complete response(pCR) in the breast and axilla (ypT0/is ypN0) as determined by a local pathologist after surgery, assessed using a modified intention-to-treat analysis. To test for non-inferiority, we used a closed test procedure, considering the nab-paclitaxel group non-inferior to the docetaxel plus carboplatin group if the lower 95% confidence interval(CI) for the odds ratio (OR) was above 0.802, which accounted for a 5.5% non-inferiority margin (10% of the 55% pCR rate for docetaxel plus carboplatin and dual HER2 blockade regimen). We planned to test for superiority only if the non-inferiority test was positive, using an alpha value of 0.05. Safety was assessed in all patients who received the study drug. The trial is registered with ClinicalTrials.gov, with the registration number NCT04547907. Findings: Between September 10, 2020, and March 1, 2023, we randomly assigned 689 women, of whom 669 started treatment (332 with nab-paclitaxel and 337 with docetaxel plus carboplatin). The nab-paclitaxel group had a higher proportion of patients achieving a pCR (220 [66.3%, 95% CI 61.2-71.4]) compared to the docetaxel plus carboplatin group (194 [57.6%, 52.3-62.9]). The OR for pCR was 1.448 (95% CI 1.058-1.981), indicating a statistically significant difference (unadjusted p=0.021). Overall, 228 (34.1%) patients were noted to have at least one grade 3 or 4 event, 100(30.1%) in the nab-paclitaxel group and 128 (38.0%) in the docetaxel plus carboplatin group (P=0·032). The most common grade 3 or 4 events overall were nausea (98[14.6%] of 669 patients), diarrhea (80 [12.0%]), and neuropathy (51 [7.6%]).However, no treatment-associated deaths were identified. Conclusions: In neoadjuvant treatment of HER2-positive EBC, 18 weeks of nab-paclitaxel monotherapy combined with dual HER2 blockade has shown significantly higher pCR rates and improved tolerability compared to the standard docetaxel plus carboplatin and dual HER2 blockade regimen. These findings could potentially reshape preferences for neoadjuvant therapy in HER2-positive EBC. Patient Characteristics pCR by clinical-pathological variables Abbreviation:Nab-PHP,nanoparticle albumin-bound paclitaxel plus trastuzumab and pertuzumab; TCbHP,docetaxel plus carboplatin ,trastuzumab and pertuzumab; HR,hormone receptor; IHC,immunohistochemistry. *estrogen and/or progesterone receptor positive is classified as hormone receptor positive;estrogen and progesterone receptor negative is classified as hormone receptor negative Adverse events Abbreviation:Nab-PHP,nanoparticle albumin-bound paclitaxel plus trastuzumab and pertuzumab; TCbHP,docetaxel plus carboplatin ,trastuzumab and pertuzumab;ALT,alanine aminotransferase;AST,aspartate transaminase. Citation Format: Zhenzhen Liu, Xiuchun Chen, Jianghua Qiao, Jiao Dechuang, Chengzheng Wang, Xianfu Sun, Zhenduo Lu, Lianfang Li, Chongjian Zhang, Min Yan, Ya Wei, Chen Bo, Yueqing Feng, Miao Deng, Mingde Ma. De-escalated neoadjuvant weekly nab-paclitaxel with trastuzumab and pertuzumab in HER2-positive early breast cancer (HELEN-006):a randomized,phase 3 trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-27-05.

Abstract PO1-27-07: Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative

Abstract Background: Overexpression of HER2 is a significant prognostic and predictive factor in early breast cancer. HER2 positive tumors are those scored by immunohistochemistry (IHC) 3+ or 2+ with amplification by in situ hybridization (ISH). These tumors may benefit from HER2-targeted treatment and additionally, in early HER2-positive BC, achieving a complete pathological response after neoadjuvant treatment improves patient survival. In recent years, new anti-HER2 antibody-drug conjugates have proven effective for HER2 low BC (defined as IHC score 1+ or 2+ not amplified) in the metastatic disease setting; however, in HER2-low early BC, studies testing novel anti-HER2 antibody-drug conjugates as neoadjuvant therapy (NAT) are ongoing. Currently, we don´t know exactly whether HER2 expression can influence the pathological response rate after NAT or disease-free survival (DFS) in these patients compared to HER2-zero (IHC 0). The aim of our study is to determine the impact on response rate to NAT and survival outcomes in early HER2-negative BC. Methods: We conducted a retrospective study in two hospitals in Andalucia, Spain. Patients with early HER2 negative BC treated with NAT from January 2015 to June 2022 were included. Patients were divided into HER2 low patients (IHC 1+ or 2+ not amplified) and HER2 0 (IHC 0). We collected clinical and pathological characteristics, pathological response rate using the Residual Cancer Burden (RCB) system where a complete pathological response (pCR) was defined as ypT0/ypTis and ypN0, and survival outcomes. The primary objective of the study was to analyze the pCR rate after NAT according to HER2 score, and secondary objectives were to assess disease-free survival and overall survival (DFS and OS rates). Results: 574 patients were included (100% women). 397 patients had hormone receptors (luminal BC) on these tumors, and 177 did not have them, i.e., triple-negative BC (TNBC). 225 patients were HER2-zero, and 312 patients were HER2-low (253/312 patients had luminal BC and 59/312 patients were TNBC). The pCR in HER2-low patients was 17.3% and 23.1% in HER2-zero patients (p=0.047). For luminal BC patients, the pCR was 16.7% in HER2-low tumors and 13.7% in HER2-zero tumors (p=0.29). Similarly, there was no difference in pCR rates in TNBC patients (45.8% in HER2-low and 53.8% in HER2-zero tumors, respectively, (p=0.958). The overall survival (OS) at 96 months was 88.7% (95% CI 85.6%-92%). Regarding survival outcomes, neither HER2 expression level was associated with higher 8-year DFS: 81.1% in HER2-low patients (95% CI 75.7%-86.8%) and 74.9% in HER2-zero patients (95% CI 62.3%-90.1%) p=0.64. There was no difference between histological subtypes at 8-years regarding DFS rate: 80.5% (95% CI 74.3%-87.2%) in luminal HER2-low patients and 76.3% (95% CI 60.8%-95.7%) in luminal HER2-zero patients, p=0.22; 83.8% in TNBC HER2-low (95% CI 74.5%-94.2%) and 77.5% in TNBC HER2-zero patients (95% CI 69.4%-86.6%) p=0.26. We also didn´t find significant differences in terms of OS. For HER2-low patients, the 8-year OS was 90.9% (95% CI 87%-94.9%) and for HER2-zero patients, it was 86.4% (95% CI 80.8%- 92.5%) p=0.46. There were also no differences in OS for different histological subgroups with an 8-year OS in luminal HER2-low breast cancer patients of 92.5% (95% CI 88%-96.7%) and 87% in HER2-zero (95% CI 78.9%-96.1%) p=0.91. In patients with triple-negative breast cancer phenotype, the OS was 84.2% for HER2-low (95% CI 74.5%-95.2%) and 85.3% for HER2-zero (95% CI 77.9%-93.4%) p=1. Conclusions: We found no difference in survival outcomes and response rate to conventional NAT between HER2-low and HER2-zero expression levels. Therefore, our data do not support the hypothesis of HER2-low as a biologically specific breast cancer subtype. Further research on this approach with HER2 antibody-drug conjugate schemes as an alternative to traditional NAT schemes is warranted. Citation Format: Ana Gil-Torralvo, Yeray Rodriguez, Alejandro Falcon, David Morales, Mónica Cejuela, Isabel Miras, Marta Amérigo, Manuel Ruíz - Borrego, Juan Bayo, Francisco Javier Salvador Bofill. Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-27-07.

Abstract PO4-01-05: The prognostic importance of biological pathway enrichment patterns in trastuzumab-treated early HER2-positive breast cancer

Abstract Background: Biological tumor signatures of HER2-positive breast cancer may impact patients’ response to HER2 targeted treatment and are important to investigate since there is a need for both escalation and de-escalation of HER2-directed treatments. We aimed to examine subgroups of HER2-positive tumors based on different biological pathway enrichment patterns and their prognostic value. Materials and methods: In a retrospective cohort of 388 early HER2-positive breast cancer patients treated with adjuvant trastuzumab, 356 HER2-positive FFPE samples were successfully analyzed for gene expression patterns using the Human nCounter Breast Cancer 360 panel (Nanostring Technologies). The raw data underwent extensive quality control and normalization in the nSolver software v.4.0 and its Advanced Analysis Module v.2.0 (NanoString Technologies). Unsupervised hierarchical agglomerative clustering was performed on pathway enrichment of nSolver customized biological process. Survival analysis for recurrence-free survival of pathway-driven clustered patients was examined using Kaplan-Meier and multivariable Cox regression models. Results: Four subgroups of patients with different biological pathway enrichment patterns were observed. The subgroup with the combination of low stromal and low immune biological pathways (Low_stromal/Low_immune) had a significantly worse prognosis than the High_stromal/Low_immune subgroup (RFS HR: 0.4; CI:0.2-0.9, p=0.02) and Low_stromal/High_immune subgroup (RFS HR: 0.4; CI:0.2-0.9, p=0.03). In addition, the subgroup with upregulation of both stromal and immune pathways (High_stromal/High_immune) showed a better response to trastuzumab than the Low_stromal/Low_immune subgroup even if not statistically significant (HR: 0.4; CI:0.2-1.0, p=0.06). Moreover, the clusters of upregulated immune pathways showed the highest levels of tumor infiltrating lymphocytes. Conclusions: In this trastuzumab-treated early HER2-positive breast cancer cohort, we observed four subgroups with different biological pathway enrichment patterns. The subgroup with the combination of low stromal and low immune biological pathway enrichment was associated with a poorer prognosis than those mainly enriched with either stromal or immune pathways. This study shows the diversity of biological signatures within HER2-positive breast cancer, and results could potentially be used in future studies of HER2 target treatments. External validation is motivated. Citation Format: Caroline Rönnlund, Qiao Yang, Caroline Schagerholm, Theodoros Foukakis, Irma Fredriksson, Xinsong Chen, Stephanie Robertson, Emmanouil Sifakis, Johan Hartman. The prognostic importance of biological pathway enrichment patterns in trastuzumab-treated early HER2-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-01-05.

Abstract PO4-19-01: The SURVIVE-HERoes trial – a secondary adjuvant treatment intervention study with trastuzumab-deruxtecan in patients with HER2 positive/HER2 low early breast cancer and a molecular relapse, based on a positive ctDNA result

Abstract Background: Despite current adjuvant treatment strategies, ≥ 20% of patients with early breast cancer (EBC) experience a metastatic relapse. In the new era of highly effective antibody drug conjugates (ADCs), secondary adjuvant treatment options for EBC patients at a high risk of relapse arise. The ADC trastuzumab-deruxtecan (T-DXd) has so far shown promising efficacy in patients with HER2-positive and HER2-low metastatic breast cancer (DESTINY Breast 03 and -04 trial) and is currently tested in the post-neoadjuvant setting in patients with non-pCR (DESTINY Breast 05 (TRUDY) trial). However, to successfully apply ADCs as a secondary adjuvant treatment, identification of patients who would benefit the most is required. The detection of minimal residual disease (MRD) using liquid biopsy, e.g. ctDNA, may offer a promising approach for patient selection. The efficacy of such a secondary adjuvant treatment in terms of delaying or even preventing distant metastases has yet to be evaluated in a randomized clinical trial. Trial design: The SURVIVE-HERoes trial is a prospective, randomized, open label comparative Phase III superiority trial in patients with intermediate to high-risk HER2-positive or HER2-low EBC, who participate in the large breast cancer surveillance trial SURVIVE (NCT05658172) and experience a molecular relapse as determined by a positive ctDNA result, but show no evidence of relapse or metastatic disease based on imaging by CT-scan and SPECT. In total, 180 patients will be enrolled and randomized with 2:1 allocation to treatment with T-DXd + (only endocrine therapy, if HR positive) versus standard of care (including endocrine treatment +/- CDK4/6-inhibitors or Neratinib). The treatment period lasts 12 months during which ctDNA levels will be repeatedly measured every 3 months (additional ctDNA testing will be performed at month 24 and 36). Stratification factors are HER2-, hormonal- and nodal status. Recruitment start is planned for Q1 2024. Eligibility criteria: Eligible patients are adult females/males, with HER2-positive or HER2-low EBC, as defined in the ASCO-CAP guidelines, and a positive ctDNA result (obtained in the SURVIVE study) that has to be confirmed ≤ 8 weeks before randomization. Primary anti-tumor therapy (surgery, adjuvant chemo- or radiotherapy) has to be completed ≥14 months, (postneo)-adjuvant treatment with anti-HER2-antibodies, T-DM1, Capecitabine, Pembrolizumab and Olaparib ≥ 4 weeks before randomization. Adequate bone marrow and cardiac function and no signs of ILD are mandatory. Statistics: The primary objective of SURVIVE-HERoes is the comparison of ctDNA clearance rates 6 months after randomization between the two study arms, which will be analysed using the chi square test for two independent proportions. Secondary objectives include the comparison of overall survival (OS), invasive disease-free survival (IDFS), distant disease-free survival (DDFS), distant recurrence-free survival (DRFS), breast cancer specific survival (BCSS), invasive breast cancer free survival (IBCFS) and quality of life (QoL) between the study arms as well as the safety and tolerability of T-DXd. Secondary survival endpoints will be estimated by the Kaplan Meier method and compared between the randomization arms using log-rank tests and cox regression models. Special aims: This trial is a proof of principle study with the aim to establish the efficacy of secondary adjuvant treatment with the ADC T-DXd in patients with HER2-positive/HER2-low early breast cancer, who are at high risk of relapse, as evidenced by detection of ctDNA in the blood. Conclusion: If SURVIVE-HERoes is successful, it could lead to a treatment shift towards early intervention with secondary adjuvant targeted therapies following liquid-biopsy based MRD detection. Contact: University Hospital Ulm, Dpt. Obstetrics & Gynecology, Germany, mail: studienzentrale.ufk@uniklinik-ulm.de Citation Format: Sophia Huesmann, Franziska Mergel, Kerstin Pfister, Angelina Fink, Forca Mehmeti, Peter Möller, Tanja Fehm, Volkmar Müller, Klaus Pantel, Thomas Friedl, Andreas Hartkopf, Brigitte Rack, Wolfgang Janni. The SURVIVE-HERoes trial – a secondary adjuvant treatment intervention study with trastuzumab-deruxtecan in patients with HER2 positive/HER2 low early breast cancer and a molecular relapse, based on a positive ctDNA result [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-19-01.

Abstract PO1-27-01: Comparing the Efficacy and Safety of TQB2440 versus the Reference Pertuzumab for the Treatment of HER2-Positive Early or Locally Advanced Breast Cancer: A Multicenter, Randomized, Double-Blind, Parallel-Controlled Phase 3 Trial

Abstract Background: Pertuzumab is a recombinant humanized monoclonal antibody targeting the extracellular dimerization domain II of HER2. On September 30, 2013, the FDA have granted accelerated approval of a pertuzumab regimen for neoadjuvant treatment of patients (pts) with high-risk, HER2-positive early stage breast cancer. TQB2440 is a pertuzumab (Perjeta®, Roche) biosimilar. This study aimed to compare the efficacy and safety of TQB2440 and the reference pertuzumab combined with trastuzumab and docetaxel in pts with HER2-positive early or locally advanced breast cancer. Methods: In this multicenter, randomized, double-blind phase 3 study, eligible pts were aged 18-75 with operable HER2-positive (IHC 3+ or ISH+) clinical stage II-IIIC breast cancer negative for ER/PR and had an ECOG PS of 0-1. The pts were randomly assigned to receive either TQB2440 or the reference pertuzumab (Perjeta®) (840 mg on day 1, cycle 1, followed by 420 mg on cycle 2-4, q3w) added to trastuzumab (8 mg/kg on day 1, cycle 1, followed by 6 mg/kg for cycles 2-4, q3w) + docetaxel (75 mg/m2, cycle 1-4, q3w). The pts then underwent surgery followed by adjuvant treatment with FEC regimens (fluorouracil 600 mg/m², epirubicin 90 mg/m², cyclophosphamide 600 mg/m², cycle 5-7, q3w), then TQB2440 (840 mg on day 1, cycle 8, followed by 420 mg on cycle 9-20, q3w) + trastuzumab (8 mg/kg on day 1, cycle 8, followed by 6 mg/kg for cycles 9-20, q3w) or until disease progression or intolerable toxicity. The primary endpoint was total pathologic complete response (tpCR) by independent review committee (IRC). Equivalence was established if the 90% confdence intervals (CIs) of the relative ratio [RR] within the interval of 0.76 to 1.32. Secondary endpoints included breast pathologic complete response (bpCR) by IRC, tpCR & bpCR by investigator, breast conserving surgery (BCS) rates, objective response rate (ORR), event-free survival (EFS), disease-free survival (DFS), OS and safety. Results: Between October 21, 2020, and November 21, 2022, 412 pts were enrolled (TQB2440 group, n=207; the reference pertuzumab group, n=205). Data cutoff was November 30, 2022. In the intention-to-treat (ITT) population, the tpCR by IRC of the TQB2440 group and the reference drug group were 58.94% and 58.05%, respectively. The RR was 1.02 (90% CI, 0.89, 1.16), which was within the predefined equivalence interval of 0.76 to 1.32. There was no statistically significant difference in the bpCR by IRC between the TQB2440 group and the reference pertuzumab group (67.63% [95% CI, 60.80%, 73.95%] vs. 63.90% [95% CI, 56.92%, 70.48%], P=0.4249). The BCS rate also comparable between the two groups with 13.04% (95% CI, 8.77%, 18.41%) vs. 13.17% (95% CI, 8.86%, 18.58%) (P=0.9695). Additionally, the results of the PP (per-protocol) population were similar to those of the ITT population. The incidence of treatment-related adverse events (TRAEs) and grade ≥3 TRAEs were similar between the TQB2440 group and the reference pertuzumab group with 79.71% vs. 75.98% and 49.28% vs. 41.67%, respectively. Conclusion: In patients with HER2-positive early or locally advanced breast cancer, TQB2440 demonstrated equivalent efficacy and similar safety to the reference pertuzumab. Clinical trial information: NCT05985187. Research Sponsor: Chia Tai Tianqing Pharmaceutical Group Co., Ltd Citation Format: Qingyuan Zhang, Shusen Wang, Nanlin Li, Qiao Cheng, Yu ren, Xuchen Cao, Jianjun Huang, Caigang Liu, Hongwei Yang, Limin Wei, Zhangjun Song, Huadong Zhao, Fangling Ning, Xiaojia Wang, Dehong Zou, Xiaohua Zeng, Jie Hao, Yunjiang Liu, Huijuan Wang, Nie Jianyun, Liang Li, Lina Liu, Tao Sun, Xiaobo Hu, Zhenhua Zhai, Huihua Xiong, Yuanqi Zhang, Enxiang Zhou, Jing Sun, Zhenhai Cai, Antai Zhang, Shui Wang, Junyang Mo, Qun Su, Xiuheng Qi, Guoren Zhou, Shuqun Zhang, Guozhong Cui, Wei Wang, Mingjiang Fan, Xinyu Qian, Xinhong Wu, Zhihong Wang, Jiuda Zhao, Yonghui Luo, Yanming Zhang, Fuguo Tian, Jiye Zhang, Dongning Chai, Qingshan Li. Comparing the Efficacy and Safety of TQB2440 versus the Reference Pertuzumab for the Treatment of HER2-Positive Early or Locally Advanced Breast Cancer: A Multicenter, Randomized, Double-Blind, Parallel-Controlled Phase 3 Trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-27-01.

Abstract PO1-17-03: Real-world evidence of Trastuzumab biosimilars in HER2-positive breast cancer: Evaluating utilization, efficacy, and safety in Taiwan

Abstract Purpose Biosimilars have emerged as a promising alternative to reference biologic products for the treatment of cancers and immunological diseases. With regard to breast cancer, trastuzumab, a reference monoclonal antibody biologic, has been the standard of care for early and advanced HER2-positive breast cancer since 1998. Trastuzumab biosimilars, which provide comparable efficacy at a lower cost, have the potential to reduce financial burden on patients and healthcare systems and improve patient access to HER2-targeted therapy. This study aimed to evaluate the utilization, efficacy, and safety of trastuzumab biosimilars in HER2-positive breast cancer patients at Kaohsiung Veterans General Hospital. Methods A total of 113 HER2-positive breast cancer patients were enrolled between February 2020 and December 2022 and treated with trastuzumab biosimilars (OGIVRI®, trastuzumab-dkst). Of these, 44 were in the neoadjuvant group, 27 in the adjuvant group, and 42 in the metastatic group. Clinical outcomes were evaluated, including pathological complete response (pCR) rate in the neoadjuvant group, objective response rate (ORR) and clinical benefit rate (CBR) in the metastatic group, and safety profile in all groups. Results In the neoadjuvant group, 18 out of 44 evaluable patients achieved pathological complete response after surgery, resulting in a pCR rate of 40.90%. In the metastatic group , the ORR was 57.14% and the CBR was 90.47%. Furthermore, in the metastatic group, treatment with dual blockade using biosimilars resulted in an better ORR of 62.96%. No adverse events of cardiac toxicity were reported in any group. In the adjuvant group, longer follow-up is needed to assess efficacy. Conclusions Our real-world experience suggests that trastuzumab biosimilars are a safe and cost-effective alternative to reference trastuzumab in the treatment of HER2-positive breast cancer. Biosimilar trastuzumab demonstrated efficacy in the neoadjuvant setting, while dual blockade with biosimilars resulted in better disease control in the metastatic setting. Further follow-up is necessary to evaluate the efficacy of trastuzumab biosimilars in the adjuvant setting. Citation Format: Yi-Hung Lo, Yen-Dun Tzeng. Real-world evidence of Trastuzumab biosimilars in HER2-positive breast cancer: Evaluating utilization, efficacy, and safety in Taiwan [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-17-03.

Abstract PO1-01-01: ECOG-ACRIN EA1211: Interim FDG-PET/CT for predicting response of HER2-positive breast cancer to neoadjuvant therapy (DIRECT Trial)

Abstract Background: Strategies to optimize treatment decision-making in early stage HER2-positive breast cancer are a current priority for the oncology and patient advocacy community. Recent studies suggest that early metabolic changes on FDG-PET/CT (imaging biomarker) predict response to HER2-directed therapy. The TBCRC026 trial showed that participants not obtaining a 40% reduction in SULmax by cycle 1 day 15 (C1D15) following neoadjuvant trastuzumab/pertuzumab (HP) were unlikely to obtain pCR [negative predictive value (NPV) 91%]. The ECOG-ACRIN EA1211/DIRECT trial aims to validate FDG-PET/CT as a neoadjuvant interim (niFDG-PET/CT) imaging integral biomarker in patients treated with standard HER2-directed regimens (NCT05710328). Design: EA1211/DIRECT is a multicenter, single-arm, primary imaging phase 2 study enrolling patients with stage II/III HER2-positive breast cancer. Patients undergo standard skull base-thigh FDG-PET/CT at baseline and C1D15 and receive standard of care pertuzumab-based neoadjuvant therapy followed by surgery. Eligibility: Age ≥18 years, ECOG performance status 0-2, stage IIa-IIIc, untreated HER2-positive breast cancer with known hormone receptor status, suitable to undergo FDG-PET/CT imaging and neoadjuvant therapy. Methods: ΔSULmaxD15 will be computed as: (D15 SULmax – baseline SULmax)/baseline SULmax. The primary objective is to estimate the NPV of niFDG-PET/CT for pCR using ΔSULmaxD15 of the primary breast cancer at a threshold of 40%, in patients treated with neoadjuvant HER2-directed therapy. NPV is defined as the probability that pCR will not be achieved by participants with ΔSULmaxD15 < 40%. Secondary endpoints include evaluating the sensitivity, specificity, and positive predictive value of ΔSULmaxD15 of the primary breast cancer at a threshold of 40% and the ability of the niFDG-PET/CT biomarker to predict 3-year event free survival (EFS). Sample Size: We expect that 50% of patients will not reach the ΔSULmax threshold of 40% and a pCR rate of 40-60%. The proposed sample size is 210 participants, adjusted to 235 to account for missing data in 10% of cases. Computation of exact, two-sided 95% confidence intervals (CI) for NPV determined the lower limit of the CI is at least 80% when the true NPV is at least 88%. The lower limit is 84% when the true NPV has the value of 91%, which was estimated in the TBCRC026 study. Current Status: EA1211/DIRECT was activated in May 2023 across the NCI National Clinical Trials Network (NCTN), and accrual is anticipated to complete in March 2025. Those interested in the clinical trial can email ea1211team@ecog-acrin.org. Conclusion: The EA1211/DIRECT trial is the first step in implementing a Response-Guided Treatment Strategy by validating the ΔSULmax threshold of 40% as the optimum cut point across standard of care HER2-directed neoadjuvant regimens. If EA1211/DIRECT meets its objectives, the results will be used to design clinical utility studies, and thus hoping to change practice. Citation Format: Heather Jacene, Constantine Gatsonis, Roisin Connolly, Brian Burnette, Erica Stringer-Reasor, Maeve Hennessy, Justin Romanoff, Alexander Taurone, Ciara O'Sullivan, H. T. Carisa Le-Petross, Courtney Lawhn Heath, Vered Stearns, Amy Fowler, Shou-Ching Tang, Karla A Sepulveda, Angela DeMichele, David Mankoff, Antonio Wolff. ECOG-ACRIN EA1211: Interim FDG-PET/CT for predicting response of HER2-positive breast cancer to neoadjuvant therapy (DIRECT Trial) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-01.

Abstract PS09-01: Individual patient data meta-analysis of clinical and translational biomarkers for prediction of pathological complete response (pCR) after de-escalated therapy in HER2+ breast cancer in four trials of the West German Study Group

Abstract Background Introduction of anti-HER2 therapies substantially improved outcomes for HER2-positive early breast cancer (HER2+ eBC). However, a considerable proportion of patients (pts) may still be overtreated with systemic chemotherapy (CTx) combinations. Establishing safe de-escalation strategies to avoid toxicities requires precise patient selection. Therefore, we set out to determine predictors for efficacy and survival in the unique setting of four de-escalation trials investigating short (12-week) neoadjuvant treatments (NAT) in HER2+ eBC. We investigated the prognostic ability of clinical and translational biomarkers for pCR to identify pts with the best prognosis after de-escalated systemic CTx-free NAT. Methods 756 pts who received de-escalated NAT were analyzed: trastuzumab + pertuzumab (T + P, n=92) and T + P + paclitaxel (pac, n=42) in ADAPT-HR-/HER2+ (NCT01817452); trastuzumab emtansine (T-DM1, n=118), T-DM1 + endocrine therapy (ET, n=125), and T + ET (n=129) in ADAPT-HR+/HER2+ (NCT01779206), T + P + pac (n=107) and T + P + ET (n=100) in TP-II (NCT03272477); and T + P + pembrolizumab (n=43) in Keyriched-1 (NCT03988036) in HER2-enriched (HER2-E) subtype by PAM50. The primary endpoint of each trial was pCR (ypT0/is ypN0). Survival was a secondary endpoint in all trials but Keyriched-1; survival data for TP-II are pending. Baseline gene expression was analyzed by BC360 assay; intrinsic molecular subtypes were determined using the PAM50 predictor. Stromal tumor infiltrating lymphocytes (sTILs) were evaluated at baseline and at week 3 of NAT. sTILs were categorized using a 30% threshold and the low cellularity category ( < 500 invasive tumor cells) at week 3. Prognostic markers for pCR were identified with univariate and multivariable logistic regression models with backstep algorithm excluding variables with p≥0.1; considered variables included age, sTILs (baseline, 3-weeks), cT, cN, grade, hormone receptor and HER2 status, intrinsic subtype, and standardized ERBB2 and ESR1 gene expression. These analyses were performed separately for NAT involving systemic CTx (i.e. containing pac, n=149) and systemic CTx-free NAT (n=607). Results Overall pCR rate was 39.1% (CTx: 66.4%; CTx-free: 32.5%). Multivariable analysis identified predictors of pCR after CTx-free NAT: low cellularity at week 3 (vs < 30% sTILs: OR 3.21, 95%CI 1.85-5.57), ERBB2 (OR 1.90, 95%CI 1.41-2.55), HER2 3+ (vs 1+/2+ and ISH+: OR 8.01, 95%CI 1.65-38.99), LumA/LumB/Basal subtype (vs HER2-E: OR 0.57, 95%CI 0.34-0.97), cT2 (vs 1: OR 0.54, 95%CI 0.33-0.89), and cN1-3 (vs 0, OR 0.46, 95%CI 0.27-0.78). In CTx-containing NAT, only ERBB2 (OR 2.08, 95%CI 1.28-3.40) and additionally ESR1 (OR 0.38, 95%CI 0.23-0.61) were prognostic for pCR. Updated analysis including expanded gene expression data from ADAPT-HR+/HER2+ and a prognostic score for pCR after CTx-free NAT developed using machine learning methods will be presented at the meeting. Conclusions This pooled analysis demonstrated a 66% pCR rate after a short (12-week) de-escalated NAT in HER2+ eBC. In one-third of patients (with mainly stage I cancer, higher HER2 expression by immunohistochemistry and gene expression analysis, and low cellularity at 3 weeks), pCR can be achieved without systemic CTx. Identified biomarkers could pave the way for developing new patient selection strategies to spare CTx-associated acute and late toxicities in a clinically meaningful number of patients. Citation Format: Monika Graeser, Oleg Gluz, Christine zu Eulenburg, Sherko Küemmel, Raquel von Schumann, Matthias Christgen, Rachel Wuerstlein, Enrico Pelz, Hans-Heinrich Kreipe, Peter Schmid, Marc Thill, Michael Braun, Jochem Potenberg, Claudia Schumacher, Joke Tio, Andreas Hartkopf, Marianne Just, Christian Schem, Kerstin Lüdtke-Heckenkamp, Eva-Maria Grischke, Felix Hilpert, Angela Kentsch, Ronald Kates, Ulrike Nitz, Nadia Harbeck. Individual patient data meta-analysis of clinical and translational biomarkers for prediction of pathological complete response (pCR) after de-escalated therapy in HER2+ breast cancer in four trials of the West German Study Group [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS09-01.

Abstract PO1-01-03: Pathological response according to early metabolic remission in an interim FDG-PET scan and to tumor infiltrating lymphocytes - A secondary analysis of the phase II trial ABCSG 52/ATHENE investigating atezolizumab in early HER2+ BC

Abstract Background: ABCSG-52/ATHENE investigated a neoadjuvant chemotherapy de-escalation/immunotherapy escalation approach with trastuzumab, pertuzumab, atezolizumab and epirubicin for early-stage HER2-positive breast cancer. The pathological complete response rate (pCR; ypT0/Tis, ypN0) - the primary endpoint of the trial - was 60.3% (95% CI 47.5% - 71.9%), and was higher than the predefined threshold for positivity (≥ 40%). Interestingly, higher pCR rates were observed in PD-L1 immune cell (IC) negative tumors (pCR 69.2%) as compared to PD-L1 IC positive tumors (pCR 55.2%). No new safety concerns were observed. Primary outcome data were reported at the ESMO Breast Cancer Conference 2023. Here, we present the correlation of pathological outcome according to early metabolic response in an interim fluorodeoxyglucose F18 positron emission tomography (FDG-PET) scan, and according to stromal tumor infiltrating lymphocytes (TILs) at baseline. Methods: Patients (pts) with previously untreated, histologically confirmed HER2-positive early breast cancer (EBC; clinical prognostic stage cT1c-4a-d, N0–3, M0) were randomized 1:1 to two 3-weekly cycles of a chemotherapy-free induction phase (Part 1) with trastuzumab and pertuzumab (TP) plus 1200 mg atezolizumab (TP+A), or TP alone. Subsequently, all pts received 4 cycles of TP+A in combination with epirubicin 90 mg/m² (Part 2). Randomization was stratified according to baseline TILs (< 5% vs ≥ 5%), hormone receptor status (positive vs. negative), and prognostic stage (≤ IIA vs. ≥ IIB; AJCC v.8.0). An FDG-PET assessment was performed at baseline and after 2 cycles of study treatment. According to PERCIST, early metabolic responses were classified as metabolic complete response (mCR) and metabolic partial response (mPR) and association with outcome was tested with Fisher’s exact test. TIL assessment in pretreatment biopsy specimen were performed according to the recommendations from the International TILs Working Group. Lymphocytic predominant phenotype was defined as a TIL proportion of ≥ 50%. Correlation of TILs and pCR was modeled with logistic regression. Results: Overall, 58 pts were randomized to TP-A (n=29) or TP (n=29) at 9 sites. In 45 patients, a protocol predefined PERCIST assessment was available. An early mCR was achieved in 14 pts (n=14/45, 31.1%): 5 pts (n=5/21, 23.8%) in the TP group and 9 pts (n=9/24, 37.5%) in the TP-A group. Pts with and without an early mCR achieved a pCR in 92.9% (n=13/14) and 54.8% (n=17/31) of cases (p=0.016), respectively. An early mCR/mPR was achieved in 37 pts (n=37/45, 82.2%). Pts with and without an early mCR/mPR achieved a Residual Cancer Burden (RCB) class 0 or I in 89.2% (n=33/37) and 50.0% (n=4/8) of cases (p=0.024), respectively. The mean stromal TIL proportion was 23.9% in the overall population, with 22.8% in TP group and 25.0% in TP-A group. A lymphocytic predominant phenotype was seen in 10.3% of pts treated in the TP group, and 17.2% of pts treated in the TP-A group. No association between TIL proportion at baseline and pCR could be detected (OR for a 10%-point increase = 1.02, 95% CI 0.78-1.34). A moderate positive correlation between numeric values of TILs and PD-L1 ICs was observed (spearman r=0.57, P< 0.0001). Exploratory correlation analyses of PD-L1 status, TIL proportion and metabolic responses in interim FDG-PET scans will be presented at the meeting. Conclusions: In ABCSG-52, chemotherapy de-escalation with intensified immunotherapy was effective and safe. Early metabolic response assessment was feasible and predicted pathologic response; therefore, incorporation of interim FDG-PET results into de-escalation trials merits further investigation. In contrast to regimens without immune-checkpoint inhibitors, TIL proportion at baseline did not correlate with pathological outcome. Funding: Provision of IMP and financial support by Roche Austria GmbH Citation Format: Gabriel Rinnerthaler, Daniel Egle, Rupert Bartsch, Clemens Schmitt, Andreas Petzer, Marija Balic, Edgar Petru, Ursula Denison, Christian F. Singer, Vesna Bjelic-Radisic, Simon Gampenrieder, Michael Knauer, Karl Sotlar, Christine Brunner, Florian Posch, Dominik Hlauschek, Lidija Sölkner, Zsuzsanna Bago-Horvath, Martin Filipits, Manuela Gili, Michael Gnant, Richard Greil. Pathological response according to early metabolic remission in an interim FDG-PET scan and to tumor infiltrating lymphocytes - A secondary analysis of the phase II trial ABCSG 52/ATHENE investigating atezolizumab in early HER2+ BC [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-03.

Perspectives on shorter durations of anti-HER2 therapy in early-stage HER2-positive breast cancer: a patient survey.

Despite previous studies proposing shorter durations of anti-HER2 therapy for selected patients with HER2-positive early breast cancer (EBC), 12-months remains standard of care. A survey was performed to assess patient perspectives and willingness to participate in studies evaluating shorter durations of anti-HER2 therapy. Patients with HER2-positive EBC completing or having previously completed anti-HER2 therapy, were recruited by healthcare professionals at The Ottawa Hospital Cancer Centre to participate in an anonymous online survey. The primary objective was to learn about patients' perspectives on shorter durations (less than 12-months) of anti-HER2 therapy. Secondary objectives were to explore patients' interest in clinical trials of shorter durations of anti-HER2 therapy and the degree of increased breast cancer risk they would accept with a shorter treatment duration. Responses were received from 94 eligible patients. Most patients received Trastuzumab alone (78%, 73/94), while 13% (12/94) received trastuzumab and pertuzumab. Side effects were experienced by 52% (46/89), the most common being; fatigue (61%, 28/46), myalgia (37%, 17/46), and diarrhea (24%, 11/46). Most patients (88%, 78/89) did not find treatment bothersome. Regarding perspectives on shorter durations of anti-HER2 therapy, most (79%, 74/94) respondents stated they would agree to less treatment if it were possible to receive fewer treatments with the same cancer benefits. 56% of patients were interested in clinical trials, however, about half stated they would not be accepting of any increase in breast cancer recurrence risk. Trials to investigate who can safely and effectively be treated with shorter durations of anti-HER2 therapy are needed. This study provides important insights to patients' perspectives on shorter durations of anti-HER2 treatment, and their concerns regarding potential increased cancer risk with less treatment.