Real-World Outcomes of Subcutaneous PHESGO® in HER2-Positive Breast Cancer: Pathological Response, Sequencing, and Safety.

During the last decade, the introduction of agents that target the human epidermal growth factor receptor 2 (HER2), such as the monoclonal antibody trastuzumab (Herceptin; Roche, Basel, Switzerland) or the tyrosine kinase inhibitor lapatinib (Tykerb; GlaxoSmithKline, Research Triangle Park, NC), in combination with chemotherapy, has changed the course of HER2-positive breast cancer. In the metastatic setting, the addition of trastuzumab to taxanes increases progression-free survival (PFS) and overall survival (OS), whereas the addition of lapatinib to capecitabine increases PFS after treatment with regimens that include an anthracycline, a taxane, and trastuzumab. In the adjuvant setting, trastuzumab increases diseasefree survival and OS. In addition to these impressive advances, clinical research to improve the outcome in HER2-positive breast cancer is as vibrant as it has ever been. A number of important questions are being addressed at this time, including the delineation of the role of neoadjuvant (presurgical) therapy, theconceptofdualHER2receptorblockade, theidentificationof markers of sensitivity or resistance to therapy, and, finally, the study of new agents. As reported in the article that accompanies this editorial, the timely Neoadjuvant Translational Breast Cancer Research Consortium 006 (TBCRC 006) trial by Rimawi et al has addressed three of these questionsandhas identifiedonemorepiece in thepuzzle: the importance ofaddinghormonal therapyinthesubsetofpatientswithHER2-positive/ hormone receptor (HR) –positive tumors. To place this study in context, let us look at what we know today. In the neoadjuvant setting, the addition of trastuzumab to chemotherapy and maintenance for 1 year increases pathologic complete response (pCR) rates and 3-year event-free survival (EFS). And there is increasing evidence that there is a good correlation between pCR and EFS in HER2-positive disease, which has led to the acceptance of pCR as the primary end point in a number of neoadjuvant studies. If some of these studies, such as the Neo-Adjuvant Lapatinib and/or Trastuzumab Treatment Organisation (NeoALTTO) study, further confirm that pCR is a surrogate marker of EFS, improved pCR in HER2-positive breast cancer could lead to regulatory approval of novel agents in this disease. In terms of dual HER2 blockade, laboratory studies have shown that a more complete blockage of the HER2 and/or the HER signaling pathway by combining two or three inhibitors with nonoverlapping mechanisms of action improves cell death and tumor shrinkage in HER2-positive models. These preclinical findings have now been confirmed in the clinical setting. Trastuzumab and lapatinib (or trastuzumab and pertuzumab [Perjeta; Genentech, South San Francisco, CA], a humanized monoclonal antibody binding to the HER2 dimerization domain), in combination with chemotherapy, results in pCR rates of 45.8% to 51.3% compared with pCR rates of 24.0% to 29.5% with a single anti-HER2 agent combined with the same chemotherapy schedule. Moreover, the addition of pertuzumab to trastuzumab and docetaxel increases PFS and OS in first-line metastatic HER2-positive disease. These results have led to regulatory approval of pertuzumab and have placed the dual HER2 blockade with pertuzumab and trastuzumab in combination with chemotherapy as the standard of care in first-line metastatic disease. Furthermore, dual HER2 blockade strategies could also become standard of care in other settings. For example, the ongoing Adjuvant Lapatinib and/or Trastuzumab Treatment Optimisation (ALTTO) phase III trial is evaluating the adjuvant dual HER2 blockade with trastuzumab and lapatinib afterchemotherapy,andAStudyofPertuzumabinAdditiontoChemotherapy and Herceptin (Trastuzumab) As Adjuvant Therapy in Patients With HER2-Positive Primary Breast Cancer (APHINITY), a phase III trial, is also currently evaluating adjuvant trastuzumab and pertuzumab with chemotherapy. Given that the dual HER2 blockade is more efficacious that single-agent HER2 therapy, a question that arises is whether the dual blockade may eliminate the need for chemotherapy in a subset of patients. In support of this proposal, the dual HER2 blockade without chemotherapy has shown high activity in a group of patients with metastatic and primary HER2-positive breast cancer. In HER2-positive metastatic breast cancer that was previously treated with trastuzumab, the addition of pertuzumab or lapatinib to trastuzumab showed higher clinical benefit than either pertuzumab or lapatinib alone. In treatment-naive JOURNAL OF CLINICAL ONCOLOGY E D I T O R I A L VOLUME 31 NUMBER 14 MAY 1

Association of HER2DX with pathological complete response and survival outcomes in HER2-positive breast cancer

126MO HER2DX and pathological complete response in HER2-positive breast cancer: A combined analysis of 4 neoadjuvant studies

‘Small’ randomised neo-adjuvant chemotherapy trials in breast cancer reporting on pathological response: more harm than good?

Background The presence of tumor infiltrating lymphocytes (TILs) has shown positive prognostic relevance for certain subtypes of breast cancer, although its value as a predictive biomarker is still uncertain. The purpose of this study was to study the association between TILs expression with the pathologic complete response (pCR) following neoadjuvant therapy in Mexican patients with HER2+ breast cancer. Methods Retrospective cohort of patients with stage I-III HER2+ breast cancer who received neoadjuvant therapy between 2017 and 2020 at Instituto Nacional de Cancerología (INCan). We collected demographic and clinico-pathological characteristics. Stage was assigned using AJCC 7th criteria; hormone receptor (HR) and HER2 status were determined according to ASCO-CAP guidelines. Quantification of TILs was made by microscopy and stained with hematoxylin-eosin. TIL levels were defined as low (1-10%) intermediate (11-40%) and high ( >40%). Complete pathologic response was defined as the absence of invasive disease in breast and axilla (ypT0/is N0). pCR rates were compared using X2 and Fisher's exact tests according to demographic and clinicopathologic characteristics. Univariate logistic regression analysis was performed to estimate the probability of pCR according to relevant characteristics. Those parameters with p ≤0.10 on univariate analysis were included in a multivariate logistic regression model. A p< 0.05 was considered as statistically significant. Results We included 164 patients (mean age 51.0 years, SD 11.4). 86 patients (54.1%) were postmenopausal, 75 patients (47.2%) had T3-T4 tumors, 129 patients (81.1%) had positive lymph nodes, 133 patients (83.6%) presented Ki67 ≥30%, 59 patients (37.1%) had negative hormone receptors, 136 patients (85.5%) were treated with anthracyclines and 20 patients (12.6%) received dual anti-HER2 therapy with trastuzumab/pertuzumab. TIL expression was low in 84 patients (52.8%), intermediate in 47 (29.6%), and high in 28 patients (17.6%). The pathologic complete response (pCR) rate in the overall population was 50.9%. pCR rates according to the demographic and clinico-pathological features are listed in Table 1. In patients with intermediate-high TILs, pCR rates were 73.1% with trastuzumab, and 75.0% with dual HER2 blockade (p=0.91). Among patients with low TILs, pCR rates were 23.6% and 75.0%, respectively (p < 0.001). On univariate analysis, intermediate TILs (OR 3.59; 95% C.I 1.70-7.59; p= < 0.001), high TILs (OR 29.00; 95% C.I 6.40-131.37; p= < 0.001), Ki67 ≥30% (OR 2.73, 95% C.I 1.11-6.73; p=0.02), and dual anti-HER2 therapy (OR 3.31; 95% C.I 1.14-9.63 p= 0.021) were associated with a higher probability of pCR. T3/T4 tumor size (OR 0.43; 95% C.I 0.22-0.81; p = 0.009) was associated with a lower probability of pCR. Positive lymph nodes, HR status , and use of anthracyclines were not significantly associated. On multivariate analysis, intermediate TILs (OR 3.28; 95% C.I 1.46-7.32 p=.004), high TILs (OR 32.37; 95% C.I 6.84-153.04 p= < 0.001), and dual anti-HER2 therapy (OR 6.58; 95% CI 2.01-21.47 p= .002) remained significantly associated with pCR. Conclusions Intermediate/high TIL expression was significantly associated with pCR. Our results suggest that TIL expression could help select patients with locally advanced HER2+ breast cancer for treatment intensification with dual HER2 blockade in resource-limited settings. However, these findings require confirmation in larger, prospective studies before implementation into routine practice. TABLE 1. Pathologic complete response (pCR) rates according to demographic and clinical pathological features (n=164). Citation Format: Alberto Monroy Chargoy, Haydee Cristina Verduzco-Aguirre, Javier Monroy Chargoy, Jose Rodrigo Espinosa-Fernandez, Jesus Antonio Martinez Ojeda, Paula Cabrera-Galeana. Tumor infiltrating lymphocytes as a predictor of pathologic complete response to neoadjuvant therapy in 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 PS09-06.

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.

Background: HER2-positive breast cancer accounts for 15-20% of all breast cancer cases. Neoadjuvant therapy has significantly improved treatment outcomes, particularly with HER2-targeted agents such as trastuzumab and pertuzumab. Objective: To compare pathological complete response rates in stage II and III HER2-positive breast cancer patients receiving neoadjuvant therapy with or without pertuzumab. Methods: This retrospective observational study was conducted at a tertiary care hospital in Karachi. Medical records of patients aged ≥18 years with stage II or III HER2-positive breast cancer who received neoadjuvant chemotherapy between January 2022 and December 2023 were reviewed. Patients were grouped based on HER2 blockade strategy: single-agent trastuzumab versus dual-agent trastuzumab plus pertuzumab. The primary endpoint was pathological complete response (pCR). Results: A total of 79 patients were included, with 66 (83.5%) receiving dual HER2 blockade and 13 (16.5%) receiving trastuzumab alone. The pCR rate was 60.6% in the dual blockade group and 53.8% in the trastuzumab-alone group (p=0.650). However, when assessed using a three-tier classification (no response, partial response, complete response), a significant difference was observed (p=0.040), with no absolute non-responders in the dual blockade group. On multivariate analysis, ER-negative status (OR = 7.17, p=0.026), taxane use (OR = 15.13, p=0.003), and high-grade tumors (OR = 0.185, p=0.028) were significant predictors of pCR. Dual HER2 blockade was not an independent predictor (p=0.163). Conclusion: Dual HER2 blockade did not significantly increase overall pCR rates but was associated with eliminating non-response, suggesting a potential role in reducing treatment failure. ER status, tumor grade, and taxane-based regimens were key determinants of response. These findings underscore the need for individualized treatment strategies and cost-benefit considerations in low-resource settings.

De-escalated neoadjuvant pertuzumab plus trastuzumab therapy with or without weekly paclitaxel in HER2-positive, hormone receptor-negative, early breast cancer (WSG-ADAPT-HER2+/HR-): survival outcomes from a multicentre, open-label, randomised, phase 2 trial.

Background. In HER2-positive early breast cancer, neoadjuvant therapy based on dual HER2 blockade with trastuzumab and pertuzumab in combination with chemotherapy is associated with high rates of pCR. The OPTIHER-HEART trial examined the safety of the neoadjuvant dual blockade added to paclitaxel and liposomal doxorubicin (Gávila et al, SABCS 2016). In this analysis, we examined the intrinsic subtypes and immune genes in baseline and surgical samples from the OPTIHER-HEART trial. Methods.OPTIHER-HEART was a multicenter single-arm phase II study of 18 weeks of neoadjuvant pertuzumab, weekly trastuzumab, liposomal doxorubicin (50 mg/m2 every 21 days) and weekly paclitaxel 80 mg/m2 in patients with stage II-IIIB HER2-positive breast cancer. pCR was defined as absence of infiltrating tumor in the breast and axilla. The expression of 55 breast cancer-related and immune genes in baseline samples and surgical specimens was measured using the nCounter platform. Intrinsic subtypes were determined by the PAM50 gene expression predictor. Univariate and multivariable logistic regression models adjusted for tumor size, ER status, age and nodal status was performed. Results. A total of 58 of the 83 (69.8%) baseline tumor samples were available. 51.7% (n=30) were classified as HER2 enriched (HER2-E) followed by Normal-like (15.5%; n=9), Basal-like (12.0%; n=7), Luminal A (10.3%; n=6), and Luminal B (10.3%; n=6). HER2-E was the most frequent subtype in both hormone receptor (HR)-negative (50.0%) and HR-positive (52.0%) tumors. The pCR rates varied according to intrinsic subtype (p<0.001). The highest rate of pCR was observed in Basal-like (85.7%) and HER2-E (83.3%), followed by Normal-like (44.4%), Luminal A (33.3%) and Luminal B (16.6%). HER2-E tumors were associated with higher pCR rates compared to non-HER2-E tumors (83.3% vs 46.5%, unadjusted odds ratio = 5.76, 95% CI 1.71 – 19.42, P=0.004), even after adjusting for HR status, size, age and lymph node involvement (odds ratio = 13.50, 95% CI2.51 – 72.52, P=0.002). Among the 55 genes, 14 (25.5%) were statistically significantly associated with pCR in univariate analysis (false discovery rate < 1%). Genes associated with pCR were 17q12-21 amplicon genes (e.g. GRB7 and ERBB2) and immune genes (e.g. CD8A and PD1). Genes associated with residual disease were luminal-related genes (e.g. ESR1 and PGR). Among the 14 genes, only 7 (i.e. CDH3, CD8A, PD1, EGFR, ESR1, SLC39A6, NAT1) were significantly associated with pCR beyond intrinsic subtype (HER2-E vs non-HER2-E). Finally, a total of 58 of the 80 (72.5%) surgical specimens were profiled. 77% of the samples were classified as Normal-like, followed by Luminal A (20%), Luminal B (2%) and HER2-E (2%). Normal-like was identified in a higher proportion in pCR samples (90%) compared to samples with residual disease (47%) (p<0.001). Conclusion. HER2-E subtype and immune genes are independently associated with pCR after dual HER2 blockade and multi-agent chemotherapy. Subtyping of surgical specimens might provide additional response and outcome data and warrants further evaluation. Citation Format: Gavila J, Oliveira M, Pascual T, Pérez J, Canes J, González X, Paré L, Calvo I, Ciruelos E, Muñoz M, Virizuela JA, Ruiz I, Andrés R, Perelló A, Martínez J, Morales S, Marín M, Martínez D, Quero JC, Llombart-Cussac A, Prat A. Association of intrinsic subtype and immune genes with pathological complete response in the OPTIHER-HEART phase II clinical trial following neoadjuvant trastuzumab/pertuzumab-based chemotherapy in HER2-positive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-04.

647 Background: While the addition of trastuzumab to neoadjuvant chemotherapy (CTX) is well established for HER2+ BC, the use of dual agent HER2 blockade in the preoperative setting is not considered standard of care. We conducted a comprehensive systematic review and meta-analysis to evaluate the impact of neoadjuvant dual and single agent HER2 blockade on breast conserving surgery (BCS), pathological complete response (pCR) for estrogen receptor (ER)+ and ER- tumors, and impact of pCR on disease-free survival (DFS) and overall survival (OS) for HER2+ BC. Methods: Based on QUORUM guidelines, MEDLINE and Cochrane Controlled Clinical Trials Register databases were queried to identify eligible trials. Inclusion criteria were prospective, neoadjuvant trials that had at least one arm with HER2 directed therapy, and reported pCR. Pooled relative risk ratios (RRs) and 95% confidence intervals (CIs) were estimated for endpoints using the random effects model. Results: We identified 34 trials (N = 4064). High pCR rates (> 40%) were seen with anthracycline-based CTX and trastuzumab, as well as taxane based CTX alone with dual HER2 blockade. The addition of trastuzumab to CTX did not improve BCS rate (RR 1.40, CI: 0.89-2.22, p=.15), but significantly increased rates of pCR (RR 1.91, CI: 1.38-2.64, p=.0001). Similarly, dual HER2 blockade compared to trastuzumab alone did not improve BCS rate (RR 1.03, CI: 0.77-1.38, p=.84), but significantly increased rates of pCR overall (RR 1.38, CI: 1.24-1.53, p<0.00001), in both ER+ (RR 1.72, CI: 1.14-2.61, p=.01) and ER- subsets (RR 1.91, CI: 1.38-2.64, p=.0001). Higher pCR was associated with improved DFS (RR 2.29, CI: 1.27-4.12, p=.006) and OS (RR 4.61, CI: 1.46-14.56, p=.009). Conclusions: Neither the addition of trastuzumab to CTX, nor the dual-HER2 blockade compared to trastuzumab, improves rates of BCS, but both significantly improve rates of pCR, which is associated with improved DFS and OS. A subgroup of HER2+ BC patients can achieve pCR with dual HER2 blockade without dependence on anthracycline-based therapy. Predictive biomarkers are needed to improve patient selection and personalize the optimal regimen for HER2+ BC.

Neoadjuvant chemotherapy with or without anthracyclines in the presence of dual HER2 blockade for HER2-positive breast cancer (TRAIN-2): a multicentre, open-label, randomised, phase 3 trial.

TPS658 Background: Dual blockade of HER2 with the combination of trastuzumab (T) and lapatinib (L) enhances antitumor activity in HER2-positive breast cancer (BC) preclinical models due to the complementary mechanisms of action of the 2 agents. In patients (pts) with T-treated HER2-positive metastatic BC (MBC), treatment with the combination was associated with longer progression-free (PFS) and overall survival (OS) compared with L alone. In pts with stage II/III BC, preoperative treatment with the combination plus paclitaxel (P) resulted in significantly higher pathologic complete response rates compared with P combined with either agent alone. This evidence supports the concept of dual HER2 blockade as a treatment strategy for HER2-positive MBC. The present study is designed to evaluate whether the addition of L improves PFS among women with HER2-positive MBC receiving T as maintenance therapy. Methods: In this open-label, Phase III study, 280 pts will be stratified by line of treatment (first/second) and hormone receptor status (positive/negative), then randomized 1:1 to receive maintenance treatment with either L (1000 mg qd, continuously) in combination with T (6 mg/kg once every 3 weeks [q3w]) or T (6 mg/kg q3w) alone. Pts will receive study treatment until disease progression, death, discontinuation due to adverse events, or other reasons. The primary endpoint is PFS; secondary endpoints are OS, clinical benefit rate, and safety. Key eligibility criteria include pts with HER2-positive MBC who have completed 12 to 24 weeks of first- or second-line treatment with T plus chemotherapy with an objective response or stable disease at time of chemotherapy discontinuation. Pts with stable brain metastases are eligible if entering the study on second-line treatment. Efficacy endpoints will be analyzed in the ITT population. A total of 193 PFS events is required to detect a 50% increase in median PFS (hazard ratio=0.67) for L plus T compared with T alone (median PFS 27 vs 18 weeks, respectively). The hypothesis will be tested using a 1-sided test with 80% power and a type I error of 0.025. The trial is currently open for accrual in the United States and Canada.

Background: MYL-1401O, a biosimilar of trastuzumab, has demonstrated efficacy and safety equivalent to reference trastuzumab (RTZ) in clinical trials for treating human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC). This study presents a real-world analysis comparing MYL-1401O with RTZ, focusing on single and dual anti-HER2 blockade therapies. The analysis encompasses neoadjuvant and first-line palliative treatments for HER2-positive early breast cancer (EBC) and MBC patients within a single hospital in Taiwan. Methods: A retrospective analysis was conducted using medical records from Kaohsiung Veterans General Hospital. Patients treated with RTZ from January 2010 to December 2022 and MYL-1401O from January 2020 to December 2022 were included. The study focused on HER2-positive EBC patients who received neoadjuvant chemotherapy with RTZ or MYL-1401O ± pertuzumab (n = 140) and untreated stage IV MBC patients who received first-line palliative treatment with RTZ or MYL-1401O ± pertuzumab (n = 150). Primary endpoints included achieving pathological complete response (pCR) in the EBC group and progression-free survival (PFS) in the MBC group. Secondary endpoints were objective response rate (ORR), disease control rate (DCR), and cardiac safety. Subgroup analyses included patients receiving dual anti-HER2 blockade. Results: Comparable pCR rates were observed between MYL-1401O and RTZ in the neoadjuvant chemotherapy group: 42.2% (19/45) for MYL-1401O and 51.6% (49/95) for RTZ (p = 0.301). Median PFS in MBC patients was similar between groups without statistically significant difference: not reached for MYL-1401O and 14.1 months for RTZ (95% CI, 9.0-19.1, p = 0.061). ORR, DCR, and cardiac safety profiles did not significantly differ between MYL-1401O and RTZ. Conclusions: This real-world study demonstrates that MYL-1401O is as effective and safe as RTZ in Asian patients with HER2-positive EBC or MBC, supporting its clinical utility in these populations. Citation Format: Ming-Chang Tsai. Real-World Assessment of biosimilar Trastuzumab MYL-1401O vs. reference Trastuzumab in HER2-Positive Breast Cancer: Utilization, Efficacy, and Safety in Asian patients [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-12-15.

147 Background: Dual neoadjuvant HER2 directed therapy is offered only in a clinical trial setting and is not standard of care, but emerging data suggests targeting multiple mechanisms may be more effective. We conducted a comprehensive systematic review and meta-analysis to evaluate the impact of neoadjuvant dual and single agent HER2 blockade on breast conserving surgery (BCS), and on pathological complete response (pCR) for estrogen receptor (ER)+ and ER- tumors, as well as the impact of pCR on disease-free survival (DFS) and overall survival (OS) for HER2+ breast cancer. Methods: MEDLINE, EMBASE, and Cochrane Controlled Clinical Trials Register databases were queried to identify eligible trials. Inclusion criteria were prospective, neoadjuvant trials that had at least one arm with HER2 directed therapy, and reported pCR. Pooled relative risk ratios (RRs) and p values were estimated for endpoints using the random effects statistical model. Results: We identified 36 trials (N = 4130). High pCR rates (> 40%) were seen with anthracycline-based chemotherapy and trastuzumab alone, and non-anthracycline based dual HER2 blockade. The addition of trastuzumab to chemotherapy did not improve BCS rate (RR 1.40, p = 0.15), but significantly increased rates of pCR (RR 1.91, p = 0.0001). Similarly, dual HER2 blockade compared to trastuzumab alone did not improve BCS rate (RR 1.03, p = 0.84), but significantly increased rates of pCR overall (RR 1.39, p < 0.00001), in both ER+ (RR 1.72, p = 0.01) and ER- subsets (RR 1.91, p = 0.0001), with no increase in grade 3/4 toxicity (RR:1.13, p = 0.16). Dual HER-2 blockade without chemotherapy was associated with pCR in a subset (11.2% - 27%) with minimal toxicity (incidence of grade 3/4 toxicity:1-5%). Higher pCR was associated with improved DFS (RR 2.29, p = 0.006) and OS (RR 4.61, p = 0.009). Conclusions: Neither the addition of trastuzumab to chemotherapy, nor the dual-HER2 blockade compared to trastuzumab, improves rates of BCS. However,both significantly improve rates of pCR, which is associated with improved DFS and OS. Dual HER2 blockade,with endocrine therapy for ER+, could potentially lessen or even obviate the use of chemotherapy.

Background: The standard treatment for HER2-positive breast cancer is the use of neoadjuvant chemotherapy with dual HER2 blockade (trastuzumab+pertuzumab). In addition to providing equal efficacy in preventing cancer recurrence and a less invasive surgical approach, response to neoadjuvant therapy (NAT) provides prognostic information for determining further adjuvant treatment. Pathologic complete response (pCR) has become a surrogate endpoint in neoadjuvant randomized clinical trials because it has been found to correlate with better long-term treatment outcomes. Many studies are currently focused on discovering predictors of response to NAT. Metabolomics is a relatively new research field focused on the analysis of small molecules (metabolites) with promising applications in personalized medicine and oncology. Neoadjuvant chemotherapy with dual HER2 blockade has led to high pCR rates, but there is still a significant number of patients with early HER2-positive breast cancer who have a partial or no response to NAT and represent an unmet medical need. The aim of this study was to find differences in the pre-NAT serum metabolomic profile of patients who achieved pCR and those with residual disease in order to discover predictive biomarkers of response to NAT. Methods: This prospective pilot study cohort included 36 patients with HER2-positive breast cancer treated with NAT at the University Hospital Center Zagreb from August 2017 to December 2021 with prior approval of the Ethics Committee. Patients' plasma samples were collected before the start of NAT and before the last cycle of NAT. Untargeted metabolomic analysis was performed using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Multivariate statistical analyses, including principal component analysis (PCA) and partial least squares analysis (PLS-DA) models, were performed. Metabolites for which the observed Variable Influence in Projection (VIP) was higher than one were considered statistically significant. The tentative identification of metabolites was confirmed by LC−MS/MS analysis. For univariate statistical comparisons between groups Student’s t-test or Mann-Whitney U test were performed, depending on data distribution, followed by Bonferroni post hoc correction for multiple comparisons (p ≤ 0.050). Results: Of the 36 patients included in the study, 55.5% (N=20) had pCR, while 44.5% (N=16) were classified as non-PCR. PCA and PCA DA analyzes showed different plasma metabolomic profiles before NAT in the pCR group and the group with residual disease. By tentative identification of metabolites, three metabolites were found with different concentrations in the two observed groups. Ganglioside GD3 and norajmalin were significantly higher in the group with residual disease, while undecaketide was significantly higher in the pCR group. A comparison of samples before and after NAT revealed different metabolomic signatures in which discriminatory metabolites belong to different metabolic pathways. In the group with residual disease, the concentration of ganglioside GD3 was lower in control samples taken after NAT than before NAT. Conclusion: This study demonstrated that there are distinct plasma metabolomic profiles in patients with HER2-positive breast cancer who achieve a pCR on NAT and those with residual disease after NAT. Ganglioside GD3, previously linked to tumor progression and aggressiveness, could be a potential predictive marker of poor response to NAT in patients with HER2-positive breast cancer treated with dual HER2 blockade combined with chemotherapy. Citation Format: Marija Križić, Morana Jaganjac, Ana Kulić, Neven Žarković, Tajana Silovski, Marina Popović, Maja Sirotković-Skerlev, Gordana Ivanac, Krešimir Bulić, Mirna Halasz, Natalija Dedić Plavetić. Predicting the pathological response to neoadjuvant therapy using untargeted metabolomics in HER2-positive breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P3-11-06.