HER2 Overexpression Research Articles

Abstract PO3-15-09: LobSig4 is a superior and readily implementable ILC-focussed prognostic biomarker set

Abstract Invasive Lobular Carcinoma (ILC) is the most common special histological subtype of breast cancer. ILC typically present as Oestrogen and Progesterone Receptor positive cancers, without over-expression of HER2 and are defined by their invasive pattern of growth. Despite clinical and biological differences, including diverse sites of metastasis, ILC are managed in the same way as the more commonly diagnosed, Invasive Carcinomas of no special type. Previously, we derived the LobSig lobular specific gene signature in an attempt to prognosticate within an otherwise homogeneous tumour category. We showed that this set of genes could stratify Grade 2 and Nottingham Prognostic Index moderate tumours into high and low risk groups. Herein, we use a nanoString nCounter custom codeset and immunohistochemistry to validate the LobSig signature. Using a CoxBoost analysis we further refined the geneset to 14 genes of interest which we examined using Immunohistochemistry on a large panel of ILC with clinical follow up data. Four targets showed a significant association with breast cancer specific survival, with high levels correlating with the poorest outcomes. Considering the expression data for these 4 candidates together, we performed a Cox Proportional Hazard Regression resulting in a combined prognostic power of (P=0.00034, HR=8.07 (CI 2.58-25.30)), which has superior prognostic power over variables including tumor size and patient age. ‘LobSig4’ represents a readily implementable and informative biomarker set for prognostication in Invasive Lobular Carcinoma. Citation Format: Lauren Kalinowski, Jamie Kutasovic, Sriganesh Srihari, Yufan Feng, Samir Lal, Kaltin Ferguson, Haarika Chittoory, Anna Sokolova, Malcolm Lim, Priyakshi Kalita De Croft, Sunil Lakhani, Peter Simpson, Amy McCart Reed. LobSig4 is a superior and readily implementable ILC-focussed prognostic biomarker set [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 PO3-15-09.

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 PO2-04-08: Translational insights from a phase 1, first-in-human (FIH) clinical trial of the anti-HER2 CAR macrophage CT-0508 in participants with HER2 positive metastatic breast cancer and other HER2 overexpressing solid tumors

Abstract Background: In pre-clinical studies, CAR macrophages (CAR-M) phagocytose tumor cells, activate the tumor microenvironment (TME), recruit T cells, and induce anti-tumor T cell immunity. CT-0508 is a first-in-class CAR-M product comprised of autologous monocyte-derived macrophages expressing an anti-HER2 CAR. In pre-clinical models, anti-HER2 CAR-M was able to control the growth of syngeneic metastatic HER2+ breast cancer. Here we present preliminary clinical results and translational data from Group 1 of the CT-0508 Phase 1 FIH study. Methods: This multi-center, open-label study is evaluating CT-0508’s safety, tolerability, and manufacturing feasibility in 18 participants with advanced solid tumors overexpressing HER2 with progression on prior therapies. Monocytes are isolated from mobilized apheresis products, differentiated into macrophages, and engineered with an anti-HER2 CAR. Group 1 participants (n = 9) receive a fractionated dose on days 1, 3, 5 and Group 2 participants (n = 9) receive the full dose on day 1. CT-0508 is administered without preparative chemotherapy. Serial blood samples and biopsies (baseline and 2 post-treatment) are collected to investigate safety, pharmacokinetics, and mechanism of action. AU565 and 4T1-HER2 cell lines were utilized to model human and murine breast cancer, respectively, in vitro and in vivo. Results: Nine participants (6F/3M) have been treated in Group 1, comprising breast (4), esophageal (2), cholangiocarcinoma, ovarian, and parotid gland cancers, with a median age of 58. Participants had received a median of 3 (range, 2-11) prior lines of therapy; 8 had received prior anti-HER2 therapy. CT-0508 was successfully manufactured and well tolerated with no dose-limiting toxicities. Three related SAEs occurred in 2 participants: grade 1 CRS with hospitalization for monitoring and grade 2 infusion reaction that resolved within 1 hour were reported in one participant. Grade 2 CRS with fever and hypoxia occurred in another participant and resolved within ~ 72 hours. Five additional participants experienced Grade 1-2 CRS and/or infusion reactions with rapid resolution. There were no cases of Grade 3 or 4 CRS. There were no major organ toxicities. Post-infusion cytokines were transiently elevated in most participants enrolled in group 1 and were self-limiting. Four of the 7 participants evaluated had stable disease. CT-0508 was transiently detectable in the blood and was detected in the TME of 8/9 participants. CT-0508 modulated the TME, leading to myeloid cell activation, effector T cell infiltration, activation, and proliferation. TCR sequencing demonstrated newly expanding T cell clones in the blood post-treatment that accumulated within the TME, suggesting expansion of tumor-reactive T cells upon CT-0508 infusion. Data from participants enrolled in Group 1 will be presented. Most of these patients were breast cancer patients with HER2 overexpressing metastatic disease. Conclusions: CT-0508 was feasible to manufacture and had acceptable safety and tolerability. Early correlative data demonstrate trafficking, TME modulation, and induction of anti-tumor T cell immunity in participants with HER2 overexpressing solid tumors including metastatic breast cancer. The study is actively enrolling (NCT04660929). Citation Format: Yara Abdou, Joanne Mortimer, Paula Pohlmann, Melissa Johnson, Richard Maziarz, Jennifer M. Specht, Claire Dees, Naoto Ueno, Yuan Yuan, Mathew Angelos, Saar Gill, Olga Shestova, Jonathon Serody, Saul Priceman, Rehman Qureshi, Poonam Sonawane, Stefano Pierini, Maria Cecilia Oliveira-Nunes, Daniel Cushing, Michael Klichinsky, Thomas Condamine, Ramona Swaby, Kim Reiss. Translational insights from a phase 1, first-in-human (FIH) clinical trial of the anti-HER2 CAR macrophage CT-0508 in participants with HER2 positive metastatic breast cancer and other HER2 overexpressing solid tumors [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 PO2-04-08.

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 PO5-20-06: Paraneoplastic cerebellar degeneration in anti-Yo antibody and HER2-positive metastatic breast carcinoma

Abstract Paraneoplastic cerebellar degeneration (PCD) in the context of breast carcinoma affects less than 1% of patients. In most cases, breast cancer diagnosis follows several months or even years after the onset of neurological symptoms. The first association between PCD and occult gynecologic cancers (breast or ovarian) was identified in 1938 with the discovery of antibodies directed against cytoplasmic antigens of Purkinje cells (“anti-Yo antibodies”). Since then, evidence has grown significantly to support anti-Yo antibodies as excellent diagnostic markers of PCD with underlying gynecologic and breast carcinoma. This case study evaluates a 57-year-old female who initially presented with headache and subacute cerebellar ataxia. Her symptoms progressed over a period of three months with multiple falls, onset of speech difficulties, and diplopia. She also reported 30-pound weight loss, which she attributed to dieting and starting semaglutide. Magnetic resonance imaging (MRI) of the brain and spine were unremarkable and autoimmune workup was normal. Cerebral spinal fluid (CSF) and serum studies demonstrated positive anti-Yo antibodies. Computed tomography (CT) of the abdomen and pelvis showed an enlarged left axillary lymph node concerning for metastatic disease with a 1.2cm focus of asymmetric density in the central inferior left breast parenchyma. Diagnostic mammogram one year prior was reportedly normal. Ataxia symptoms improved after a course of empiric intravenous immunoglobulins and steroids. Ultrasound-guided biopsy of the left axillary lymph node revealed metastatic mammary carcinoma: estrogen and progesterone receptor negative and human epidermal growth factor receptor 2 (HER2)-positive, cT0N2aM0, ypTxN1aM0, stage IIIa (AJCC 8th edition). She underwent further metastatic workup, including repeat CSF studies and MRI. MRI of the spine was remarkable for multiple hemangiomas throughout the cervical, thoracic, and lumbar spine, with subsequent unremarkable bone scan. MRI of the abdomen was remarkable for right hepatic lobe hemangioma and a right adrenal nodule. CSF studies showed no sign of metastases. After multidisciplinary discussion, TCHP (docetaxel, carboplatin, trastuzumab, and pertuzumab) neoadjuvant therapy was initiated and repeat imaging demonstrated favorable treatment response with a shrinking axillary mass; no primary breast mass was identified. The patient underwent left sentinel lymph node biopsy with a positive frozen section intraoperative for invasive cancer, therefore proceeded with left axillary lymph node dissection. She was offered a mastectomy but elected for only axillary surgery. Pathology revealed 1 of 14 lymph nodes were positive for metastatic ductal carcinoma. She remains in a rehabilitation center and her ataxia is improving, but her functional status remains below baseline. She is undergoing radiation to whole breast and regional lymph nodes. With this case, we aim to continue to build upon the limited base of the exceedingly rare presentation of breast cancer-associated paraneoplastic syndrome. In addition, several studies and case reports have demonstrated a strong correlation between HER2 overexpression and anti-Yo associated PCD. As we continue to diagnose and monitor breast cancer patients, we could consider starting to screen for anti-Yo antibodies in HER2-positive patients to gain insight into a patient’s prognosis and development of PCD. Citation Format: You Kim, Alison Coogan, Andrea Madrigrano. Paraneoplastic cerebellar degeneration in anti-Yo antibody and HER2-positive metastatic breast carcinoma [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 PO5-20-06.

Abstract PO5-04-02: Combination of trastuzumab competing and non-competing fully human internalizing anti-Her2 monoclonal antibodies drug conjugates increases their inhibitory effect on the growth of HER2 positive metastatic breast cancer cells

Abstract The human epidermal growth factor receptor (HER) family of receptors plays a key role in proliferation stimulator for several human cancers. In particular, HER2 is overexpressed in 15-30% of breast cancers with or without gene amplification with prognostic and predictive implications. HER2 overexpression is associated with shorter disease-free and overall survivals, resistance to hormonal agents and increased risk of brain metastasis. Trastuzumab is a humanized anti-HER2 monoclonal antibody that binds to domain IV of HER2 extracellular domain and blocks its signaling. More recently, two antibody drug conjugates using trastuzumab have been approved: Ado-Trastuzumab-Emtansine (Kadcyla) consisting of trastuzumab conjugated to the drug mertansine DM1 and fam-trastuzumab-deruxtecan-nhki (Enhertu to deliver the topoisomerase inhibitor deruxtecan. We are reporting here the development of fully human internalizing anti-HER2 antibodies with distinct epitopes on the HER2protein which compete or not with trastuzumab for binding to HER2. These monoclonal antibodies have been developed by immunizing fully human (TC-Mab mouse) mice with recombinant HER2 protein. After production of hybridoma secreting fully human immunoglobulins, the screening process included competition with trastuzumab for binding to Her2 by enzyme linked immunoassay and Octet epitope binning and affinity determination as well as internalization assay. Several internalizing antibodies able to compete or not with trastuzumab and with high affinity (Kd ranging from 10−9 M to 10−12 M) were selected. Their ability to deliver a cytotoxic payload in HER2 overexpressing breast cancer cells such as SKBR3, BT474 and AU565 was next investigated. Two groups of antibodies: one competing with trastuzumab and the other one non-competing were further characterized. Data related to these antibodies’ biochemical characteristics as well as their ability to inhibit proliferation in vitro and in vivo in mouse xenografts studies will be presented here. In conclusion, the use of fully human mice to develop monoclonal antibodies provides a powerful and attractive approach to develop fully human monoclonal antibodies against cancer targets by-passing the need for humanization and affinity maturation of antibodies. This work is supported by 5R44CA224718 SBIR grant from the National Cancer Institute. Citation Format: Ginette Serrero, Binbin Yue, Jianping Dong, Jun Hayashi. Combination of trastuzumab competing and non-competing fully human internalizing anti-Her2 monoclonal antibodies drug conjugates increases their inhibitory effect on the growth of HER2 positive metastatic breast cancer cells [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 PO5-04-02.

Abstract PO1-08-06: Clinical-molecular correlation in breast cancer with pathogenic variants in CHEK2. Is there a relationship with HER2+ breast cancer?

Abstract Background: The CHEK2 gene codes for checkpoint protein Kinase 2 (CHK2), an effector in the ATM-CHK2-p53 DNA damage repair pathway in double-stranded DNA breaks. Initially, germline pathogenic variants were associated with moderate risk for breast carcinoma, but later studies linked alterations in the gene to other types of cancer. The aim of our study was to establish a clinical-molecular correlation of profiles of patients carrying pathogenic variants and variants of uncertain significance (VUS) in CHEK2 with a diagnosis of breast carcinoma, in patients treated in our hospital. And to describe whether the pathogenic variant c.1100del present different clinical or immunohistochemical characteristics than the rest, also considering the particularity of being an island population. Methodology: We have collected data from genetic studies performed in patients from our hospital, covering a population of 580,000 inhabitants, in Santa Cruz de Tenerife ( Canary Islands, Spain), between 2017 and 2023.Out of 952 patients with suspected hereditary cancer, 81 had CHEK2 mutations. In patients with CHEK2 mutations and breast cancer we established three groups for clinical molecular analysis: 1) pathogenic variant c.1100del, 2) other pathogenic variants and 3) VUS, to be correlated with age, histology, ER, PR, Ki, grade (G), HER2, second tumour or recurrence, subtype, HER2 low, aggressive clinic, neuropathy, haematological and digestive toxicity. The germline genetic study performed covered 77 genes related to hereditary cancer using the SureSelect HS library preparation kit (Agilent Technologies). The classification of the variants identified was performed according to the American College of Medical Genetics (ACMG) criteria. Results: In the 952 genetic studies performed, 8.5% of cases had CHEK2 mutations, 2.62% were related to breast carcinoma (N=26) of which 54% had the pathogenic variant “c.1100del”, 16% “other” pathogenic variants and 30% VUS. The mean age at diagnosis was 42 years, being lower than 38 years in pathogenic variants other than c.1100del. Histologically, infiltrating ductal carcinoma (85%) and mucinous carcinomas (12%), ER+ (93%), PR+ (77%), HER 2+ (31%), HER2 low (44%), G2-3 (84%) and Ki >15% (70%) were predominant. Second diagnoses were tumour or recurrence in 40%, being higher in the group of pathogenic variants other than c.1100del (50%), and showing aggressive clinical course in 26%. The predominant subtype was luminal B (50%), HER2+ (31%), luminal A (12 %) and triple negative (7%), although in the cluster analysis patients with pathogenic variant c.1100del HER2+ were higher (38%) and luminal B (38%), while in pathogenic variants other than c.1100del and VUS the luminal subtype was predominant (75%). Chemotherapy toxicity: neuropathy (35%), haematological and digestive toxicity (50%). Conclusion: Our results are consistent with other reported series, being related with all breast carcinoma subtypes, mainly luminal B and HER2+ and with triple negative at a lesser extend. Considering HER2 low patients were about 75% of patients with CHEK2 mutations, a molecular mechanism that correlates a truncating mutation in CHK2 and HER2 overexpression can be hypothesized. In the cluster analysis, HER2+ (38%), and luminal B (38%) subtypes predominate in patients with pathogenic variant c.1100del, while in pathogenic variants other than c.1100del and VUS the luminal B subtype predominates (75%), as well as recurrence or second tumours in 50% of cases. On the other hand, considering that this is an island population, the possible effect of geographical isolation and the resulting inbreeding in the past, these facts do not seem to elicit differences comparing to the rest of the continental population, although the increase in pathogenic variants in CHEK2 were observed in patients from the small island of La Gomera. The relationship between CHEK2 and HER2 in breast cancer is an area of active research. Relative frequency in groups of CHEK2 variants Relative frequency in CHEK2 “ pathogenic variants c.1100 del (53%)”, “other”pathogenic variants no c.1100 del (15 %)" and VUS (30%). Relative frequency of breast cancer subtypes according to CHEK2 variants. HER2+: 30,8%. Luminal A: 11,5% . Luminal B: 50%. Triple negative: 7,7% . Histology, ER, PR, Ki, HER2 and HER2 low Histology , infiltrating ductal carcinoma (84%), ER+ (92%), PR (77%), Ki >15% (70%), HER2+ (31%), HER2 low (45%) Citation Format: Natalia Pérez-Rodríguez, Carol Prieto-Morin, Maria del Carmen Maeso, Lina Pérez-Mendez. Clinical-molecular correlation in breast cancer with pathogenic variants in CHEK2. Is there a relationship with HER2+ 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 PO1-08-06.

Abstract PO5-06-09: Metastatic triple negative breast cancer has distinct tumor immune landscape

Abstract Background: Triple negative breast cancer (TNBC) is considered the most immunogenic breast cancer subtype due to higher levels of tumor infiltrating immune cells (TILS), elevated tumor mutational burden and PD-L1 expression, providing a rationale for immunotherapy. Here we aimed to investigate the differences in the immune microenvironment of primary vs. metastatic sites in TNBC vs. non-TNBC and their impact on survival. Methods: Comprehensive immune profiling, including PD-L1 IHC and the expression of 395 immune genes, was performed on 147 real-world FFPE breast cancer samples (32 primary, 115 metastatic). 37 samples were, by definition, triple negative for ER, PR, and HER2 overexpression. PD-L1 (CPS positive ≥1% and CPS positive ≥10%) was determined using immunohistochemistry (22C3). mRNA expression signatures of tumor inflammation (TIGS, weak/moderate/strong) and cell proliferation (CP, poor/moderate/high) were determined by RNA-sequencing. Demographic and clinicopathologic variables were collected. Statistical comparisons of biomarkers between groups were calculated using the Wilcoxon Rank-Sum test for continuous variables and the proportions test for categorical variables (p≤0.05 for significance). Survival differences were quantified by Cox proportional hazards analysis (p≤0.05 for significance). Results: Triple negative status was associated with current use of alcohol [p=0.03]. Black patients were also more likely to have TNBC, constituting 24% of TNBC patients while only making up 14% of the total cohort [p=0.04]. Conversely, white patients were less likely to have TNBC, constituting 73% of TNBC patients while making up 84% of the total cohort [p=0.04]. Comparing TNBC and non-TNBC cases, TNBC cases were observed to have significantly higher TIGS [p=0.014] and PD-L1 expression [p=4.4 × 10−7]. Additionally, TNBC cases trended towards exhibiting greater cell proliferation [p=0.069]. These differences were found to be driven primarily by metastatic tumors, among which TNBC tumors showed significantly higher TIGS [p=0.015], cell proliferation [p=0.021], and PD-L1 expression [p=2.9 × 10−7] than non-TNBC tumors, while none of these significant associations were observed among primary tumors. Triple negative status was significantly associated with PD-L1 expression (assessed by IHC), with a majority of PD-L1 positive cases determined to be triple negative [70% of CPS≥1% cases, p=5 × 10-5; 59% of CPS≥10% cases, p=6 × 10−4]. Several immune-related genes and immune checkpoint molecules were over-expressed in triple negative breast cancer, including CD8, GZMB, PRF1, CCL5, IFNG, TIGIT and CXCL10. A number of genes were also significantly overexpressed in metastatic tumors: KRT5 [p=0.02], TFRC [p=0.04], ABCF1 [p=0.04], FCRLA [p=0.05], LAMP3 [p=0.05], and underexpressed in metastatic tumors: ENTPD1 [p=0.05], IGSF6 [p=0.03], and ITGA1 [p=0.03]. Conclusions: Our comprehensive biomarker analyses showed that metastatic TNBC has a more inflamed tumor microenvironment and higher checkpoint target expression compared to non-TNBC. Further analysis of immune expression by site-specific metastases and correlation with immunotherapy outcomes is warranted to guide clinicians in selection of the ideal metastatic site to biopsy for therapeutic decision making. However, in a collective TNBC context, these data support the use of immunotherapy in metastatic TNBC. Citation Format: Robert Seager, Heidi Ko, Sarabjot Pabla, Maria-Fernanda Senosain, Erik Van Roey, Shuang Gao, Kyle Strickland, Rebecca Previs, Mary Nesline, Stephanie Hastings, Shengle Zhang, Jeffrey Conroy, Taylor Jensen, Marcia Eisenberg, Brian Caveney, Eric Severson, Shakti Ramkissoon, Shipra Gandhi. Metastatic triple negative breast cancer has distinct tumor immune landscape [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 PO5-06-09.

Abstract PO1-04-02: ACE-Breast-03: A phase 2 study of ARX788, a novel next-generation anti-HER antibody-drug conjugate in HER2-positive metastatic breast cancer patients previously treated with trastuzumab deruxtecan

Abstract Background: HER2 overexpression and/or amplification confers aggressive tumor behavior and decreased survival in patients with breast cancer. Targeting of HER2 is a validated therapeutic strategy, and trastuzumab deruxtecan (T-DXd) has emerged as a preferred treatment in the second-line setting. However, effective treatment following progression on T-DXd remains a major unmet medical need. ARX788 is a next-generation antibody-drug conjugate (ADC) using a technology platform whereby a HER2-specific monoclonal antibody is conjugated to amberstatin 269 (AS269), a potent cytotoxic tubulin inhibitor. Site-specificity, high homogeneity, and stable covalent conjugation of ARX788 leads to the slow release and prolonged peak of serum pAF-AS269, which may contribute to the lower systemic toxicity and increased targeted delivery of payload to tumor cells, at a lower effective dose compared with other HER2 ADCs. Methods: ACE-Breast-03 (NCT04829604) is a global, phase 2 study designed to assess anticancer activity and safety in approximately 40 patients with unresectable or metastatic HER2 positive breast cancer who have been previously treated with T-DXd. Eligibility criteria include measurable disease by RECIST v1.1, radiographically stable brain metastases, no more than three prior lines of treatment in the metastatic setting, and HER2 positivity as determined by central review. If recently progressed on T-DXd or trastuzumab emtansine (T-DM1), a new biopsy for HER2 status is required. Patients will be administered 1.5 mg/kg of ARX788 every three weeks. Efficacy will be assessed using RECIST v1.1 at nine-week intervals after starting ARX788 until progression or start of new cancer treatment. Objective response rate is the primary endpoint, with disease control rate, progression-free survival, overall survival, best overall response, duration of response, and time to response as additional endpoints. The safety and tolerability profile will also be evaluated. PK analysis will determine serum concentrations of ARX788, total antibody, and pAF-AS269. Potential predictive and/or prognostic biomarkers will be analyzed for exploratory purposes. Descriptive statistics will be used to evaluate anticancer activity, safety, and tolerability. The study is currently recruiting patients. Citation Format: Kashif Ali, Laila Agrawal, Anu Thummala, Kevin Kalinsky, Sami Ali, Sibel Blau, Margaret Block, Michael Danso, Denise Yardley, Jay Andersen, Adrienne Gropper-Waks, Priya Jayachandran, Igor Makhlin, Petros Nikolinakos, Joyce O'Shaughnessy, Sandra Aung, Colin Hessel, Hope Rugo, William Gradishar, Debu Tripathy. ACE-Breast-03: A phase 2 study of ARX788, a novel next-generation anti-HER antibody-drug conjugate in HER2-positive metastatic breast cancer patients previously treated with trastuzumab deruxtecan [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 PO1-04-02.

Abstract PO2-18-08: Identification of novel genetic/therapeutic vulnerabilities in breast cancer

Abstract Background: Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer death among women worldwide. Triple negative breast cancer (TNBC) is an aggressive subtype that is defined by the lack of expression of estrogen and progesterone receptors in the absence of HER2 amplification or overexpression. TNBC represents 15-20% of all breast cancers and occurs more frequently in young premenopausal women. TNBC often ends with a poor clinical outcome due to high histological grade, rapid recurrence in many patients combined with few treatment options. These realities highlight the urgent need to identify novel therapeutics vulnerabilities that can be leveraged to improve TNBC patient outcomes. Methods: We utilized the publicly available DepMap and Kaplan Meier datasets to identify essential genes that were unique to TNBC cells and whose expression levels were associated with worse patient outcomes. siRNA based approaches were used to confirm the relevance of top hits in mediating cancer cell phenotypes including viability, cell-cycle profiles and induction of apoptosis among others. A novel drug currently being developed was identified for the top hit in these studies and was subsequently employed in multiple in vitro approaches to characterize the mechanisms of action in TNBC as well as initial efficacy studies using clinically relevant ex vivo patient derived models. Results: Using the DepMap database, we interrogated genome-wide sgRNA knockout screens conducted in over 40 breast cancer cell lines to identify specific genes whose expression was required for cell viability in TNBC cells, but not other breast cancer cell lines. This endeavor identified 6 genes (CTPS1, HUS1, PRKRA, RAD1, RAD9A and RHOA) that were preferentially essential in TNBC cells. Further profiling of these genes revealed that CTPS1 expression is higher in cancer relative to normal tissue and that its expression is further upregulated in chemotherapy- and PARPi-resistant models. Knockdown of CTPS1 in TNBC cells was shown to decrease cell proliferation and viability with no effects observed in estrogen receptor+ cell lines. Using a first-in-class, highly selective and orally bioavailable CTPS1 inhibitor (STP938) developed by Step-Pharma, we identified IC50s in the low nM range for many TNBC cell lines, including cell models that are resistant to existing standard-of-care therapies. Inhibition of CTPS1 was shown to arrest cells in S phase. Conclusions: Our studies have identified CTPS1 as an essential gene in TNBC. CTPS1 encodes an enzyme responsible for the catalytic conversion of UTP (uridine triphosphate) to CTP (cytidine triphosphate), an essential step in the biosynthesis of nucleic acids. These findings are timely in light of the recent and ongoing development of the first-in-class CTPS1 inhibitor, STP938, for which first-in-human studies are underway for refractory B- and T-cell lymphomas. Based on our initial studies using this drug, we provide pre-clinical evidence of its efficacy in multiple models of primary and advanced TNBC. Efforts are currently underway to move this work toward a clinical trial for TNBC patients. Citation Format: Xiyin Wang, Michael Emch, Lauren Voll, Rebecca Russell, Esther Rodman, Philip Beer, John Hawse. Identification of novel genetic/therapeutic vulnerabilities in 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 PO2-18-08.

Abstract PO3-20-07: Five years and counting: A case of a 47-year-old female with De Novo Metastatic HER2 positive disease on multiple lines of treatment

Abstract HER2-positive breast cancer refers to a specific subtype of breast cancer characterized by the overexpression or amplification of the human epidermal growth factor receptor 2 (HER2) protein on the surface of cancer cells. The overexpression of HER2 leads to increased signaling pathways that promote cell growth and division, making HER2-positive breast cancer inherently more aggressive compared to other subtypes. The aggressive behaviour of HER2-positive disease may be attributed to its rapid cell growth, high metastatic potential, and increased risk of recurrence. Fortunately, there are targeted therapies that specifically inhibit the HER2 protein. These targeted treatments help to block HER2 signaling, slow down tumor growth, and reduce the risk of recurrence. We report a case 47 year old premenoapausal Filipino female diagnosed with de-novo metastatic HER2-positive breast cancer with liver and lung metastasis in 2018. Advised Pertuzumab Trastuzumab and Taxane therapy but due to financial constraints was amenable only to Trastuzumab and Paclitaxel. During treatment noted symptomatic cardiac decline, hence shifted to Lapatinib & Capecitabine, tolerated well with stable disease for 1 year. Disease then progressed to the contralateral breast, given 6 cycles of Ado Trastuzumab Emtansine with partial response followed by modified radical mastectomy of the right and toilet total mastectomy of the left breast. She was lost to follow up. Her cancer recurred 1 year later as skin lesions on chest wall. She was given 6 cycles of Ado Trastuzumab Emtansine, however still with progression as skin lesions on the chest. Patient was then given 5 cycles of Trastuzumab with Eribulin. Despite treatment, there was progression with symptomatic brain metastasis and further increase in size and number of skin metastasis of the chest wall. Lesions were noted to be ulcerating and bleeding. Hence patient underwent 5 of 5 sessions of Fractionated stereotactic radiation therapy and 10 of 10 sessions of palliative radiotherapy to the chest wall. Patient was then given Pertuzumab & Trastuzumab with note of improvement of chest wall lesions. However, after 7 cycles of treatment, noted progression again as skin metastasis on the chest wall. Hence patient was shifted to Trastuzumab Deruxtecan. At the time of writing, the patient has had a good response with Fam-Trastuzumab Deruxtecan-nxki with partial resolution of her skin metastases on the chest with stable disease of lung and brain target lesions. No bleeding or ulcerations of the lesions and no recurrence of dizziness or imbalance reported. The patient will continue to receive Fam-Trastuzumab Deruxtecan-nxki until disease progression and/or unacceptable toxicity. Here we have a case of patient with extended survival after being fortunate to have received multiple lines of treatment for the disease. In this case we were able to apply the advances of research in HER2-positive breast cancer and see it in the clinical setting. Thus, ultimately translating to extended overall survival for the patient. We see the importance of continuous research on HER2-positive breast cancer disease and how these studies have helped us in overcoming treatment resistance, understanding disease progression, tailoring of therapies to individual patients, optimizing treatment outcomes, developing new therapies, and enhancing the quality of life for patient. Ongoing research continues to explore new therapeutic approaches and strategies to further improve outcomes for individuals with metastatic HER2-positive breast cancer. This is truly an exciting time for cancer research because what used to be a very deadly disease is now becoming something that we are able manage. Citation Format: Sofia Dominique Unson, Rubi Li. Five years and counting: A case of a 47-year-old female with De Novo Metastatic HER2 positive disease on multiple lines of treatment [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 PO3-20-07.

Abstract PO1-02-07: HER2 Low Non-Metastatic Breast Cancer in Qatar: A Nationwide Retrospective Cohort Study to Evaluate the Response to Neoadjuvant Chemotherapy: A Real-World Analysis

Abstract Background: Breast Cancer is the most diagnosed cancer type worldwide and the second leading cause of cancer-related death among women. HER2-low breast cancer is a newly defined molecular subtype of breast cancer in which tumors exhibit a minimal overexpression of HER2 or no gene amplification. To illustrate, HER2-low tumors typically have an IHC score of 1+ or a score of 2+ with negative amplification. However, emerging evidence suggests that even a minimal amplification of HER2 may significantly impact the response to therapy and prognosis. Our study aims to unveil the impact of HER2-low expression on the response to anthracycline and taxane-based neoadjuvant chemotherapy (NACT) in comparison to the HER2-negative group in non-metastatic breast cancer. The primary objective was evaluating the response to NACT comparing the favorable response (complete and partial response) in each of the two groups of HER2-low and HER2-negative patients. Methods: This is a retrospective cohort study. All patients’ profiles with non-metastatic, HER2-Low, and HER2-negative breast cancers who received neo-adjuvant chemotherapy and underwent surgery between the 1st of January 2018 and the 30th of August 2022 were included. Patients' response was evaluated using surgical pathology reports to compare the two study groups (HER2-low and HER2-negative). Results: The total number of patients included was 262 patients, the majority were HER2-low 89% (233/262) vs. 11% (29/262) HER2-negative. A favorable response to NACT was shown in 71% (185/262) of all patients. The favorable response rate was similar in both groups, 70% (164/233) in the HER2-low group vs. 72% (21/29) in the HER2-negative group, OR: 1 (95% CI: 0.8-1), p-value 0.8. Similarly, the pathological complete response (pCR) rate was the same in both study groups at 14%, OR: 0.7 (95% CI: 0.2-3), p-value: 0.6. Interestingly, patients with hormone-positive tumors across both study groups had a higher response rate as compared to hormone-negative patients. However, statistical significance was shown in the HER2-low group only. In the HER2-low cohort, 73% of the patients (119/164) with hormone-positive tumors showed a favorable response OR: 0.8 (95% CI: 0.8- 1), p-value: 0.001. Comparatively, in the HER2-negative cohort, 52% of the patients (11/21) with hormone-positive tumors had a favorable response OR: 2 (95% CI: 1– 5), p-value: 0.05. Conclusion: Our results did not show any significant impact of HER2-low expression on neoadjuvant chemotherapy response. Nonetheless, a statistically significant difference in response was observed in the hormone-positive HER2-low breast cancer patients. Further studies are needed to evaluate the influence of hormonal expression on the response rate to NACT in the HER2-low patient population. Citation Format: Ahmed Kardousha, Wafaa Shehada, Ahmed Basha, Sahar Nasser, Mufid el Mistiri, Anas Hamad, Salha Al-Bader, Shereen Elazzazy. HER2 Low Non-Metastatic Breast Cancer in Qatar: A Nationwide Retrospective Cohort Study to Evaluate the Response to Neoadjuvant Chemotherapy: A Real-World 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 PO1-02-07.

Abstract PO5-17-10: PERFORMANCE AND OUTCOMES OF THE 70-GENES SIGNATURE (MAMMAPRINT™) IN A POPULATION WITH MIDDLE INCOME – REAL WORLD STUDY (AGEMA-BRA)

Abstract INTRODUCTION – Breast cancer remains the most frequent tumor in the female population and the fourth in mortality in the world population (GLOBOCAN 2020). With the aim of reducing mortality and at the same time de-escalating treatment, avoiding overtreatment, individualized therapy is increasingly being applied. The genomic signature of 70-genes, when stratifying patients into high and low risk of relapse, makes it possible to withdraw part of the cases of high clinical risk from chemotherapy treatment. However, the MINDACT study, which validated this signature, was carried out only in the European population, with no data on performance and outcomes in other populations with greater miscegenation. OBJECTIVE – To study the performance and outcomes of the 70-gene genomic signature (MammaPrint™) in a Brazilian population with a high ethnic miscegenation. METHODOLOGY – A retrospective cohort study was conducted in 953 women with breast cancer at high clinical risk, who underwent genomic analysis with the 70-gene platform (MammaPrint™), from January 2016 to December 2020. For the statistical evaluation, a descriptive analysis of the data with absolute and relative frequencies of the variables was performed. To verify the association between qualitative variables, the chi-square test was used. All analyzes were performed in the R 4.1.0 environment (R Core Team, 2021). Study approved by the Research Ethics Committee of the State University of Ponta Grossa (PR) - (CAAE: 12194219.4.0000.0105). RESULTS – The analysis of 955 cases from the AGEMABRA cohort (all at high clinical risk) showed 546 cases (57.2%) with low genomic risk and 409 cases (42.8%) with high genomic risk to MammaPrint™ (MP); when compared with data from the MINDACT study (46.2% low risk and 53.8% high risk) a significant difference was observed in the distribution for high and low risk in the two populations (p.< 0.001). After excluding patients with missing data, 409 cases of low- and high-risk MP were studied. The variables regarding age group, tumor diameter, number of affected lymph nodes, hormone receptors and HER2 overexpression showed no significant difference; within this same analysis, the tumor grade showed a higher incidence of grade 1 in the population with low genomic risk (6.6%) compared to high risk (2.9%) and grade 3 in high risk (13%) compared to low risk (5%) with p.< 0.001 (table 1). With an average follow-up of 40 months, the DMFS (disease metastatic free survival) found was 97.2%, being 97.8% for low risk and 96.2% for high risk (p.0.54). All patients with high-risk MP who progressed had used adjuvant chemotherapy, and all patients with low-risk MP who relapsed received only endocrine therapy. When compared to the MINDACT population, the AGEMA-BRA has more elderly patients, and smaller tumors with a lower histological grade (p.=< 0.001). CONCLUSION – The analysis of the Brazilian population submitted to the 70-gene genomic signature showed a greater proportional number of tumors with low genomic risk than in the test approval study, favoring its application with the aim of de-escalating systemic treatment in this population. Despite the low rate of disease progression in the AGEMA-BRA study, probably determined by the population with the best prognosis disease and the short follow-up, recurrence was similar in the high and low genomic risk groups, demonstrating the adequate selection of systemic therapy following the results of the MP. An increase in the sample size and longer follow-up are necessary to confirm the results found. Table 1. Characteristics of patients and tumor according to risk (AGEMA-BRA) Citation Format: Fabio Mansani, Ruffo Freitas-Junior. PERFORMANCE AND OUTCOMES OF THE 70-GENES SIGNATURE (MAMMAPRINT™) IN A POPULATION WITH MIDDLE INCOME – REAL WORLD STUDY (AGEMA-BRA) [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 PO5-17-10.

Abstract PS09-03: Neoadjuvant zanidatamab for stage I node negative HER2 positive breast cancer

Abstract Background: The addition of trastuzumab+/-pertuzumab to chemotherapy has changed the natural history of earlyHER2+ breast cancer. However, trials with targeted therapy alone are needed to avoid acute and chronic toxicities of chemotherapy. Zanidatamab is a novel, humanized, bispecific, immunoglobulin G isotype 1-like, monoclonal antibody directed against the juxtamembrane extracellular and dimerization domains (ECD2, ECD4) of HER2. The biparatopic nature of zanidatamab results in HER2 clustering that modulates signaling and leads to immune activation. Zanidatamab has demonstrated antitumor activity in heavily pre-treated HER2 overexpressing metastatic breast cancer with an acceptable safety profile. We hypothesized that zanidatamab would be a safe and effective regimen for women with node negative stage I HER2+ BC. Methods: Patients with 1-3 cm, clinically node negative HER2+ BC were enrolled in a single-institution investigator-initiated clinical trial. Patients had HER2+ breast cancer: HER2 3+ by IHC or IHC 2+ and ISH +. Patients received six to ten doses of zanidatamab, 20 mg/kg IV every 2 weeks prior to surgery. Patients with ER+ tumors also received neoadjuvant endocrine therapy. Post-menopausal patients received letrozole 2.5 mg daily, and pre-menopausal patients received tamoxifen 20 mg daily or GNRH and letrozole 2.5 mg. The primary objective was to evaluate efficacy as determined by pathologic complete response (pCR). Secondary objectives included pathologic response by residual cancer burden (RCB), radiological response, and safety profile of zanidatamab. Results: Twenty patients with HER2+ breast cancer were enrolled. Median age was 62 years old (range 30-73). Fifteen patients had HER2 3+, and 5 HER2 2+/ISH+ tumors with a median size of 1.95 cm (range 1-3 cm) and 10 patients had tumors >2 cm. Seven patients were pre-menopausal. Six received tamoxifen and 8 letrozole. Eleven patients completed 6 cycles and 9 patients will receive 10 cycles of zanidatamab. Eleven patients already had surgery the remainder patients will have surgery by Oct 30, 2023. Four (36%) had pCR, 3 RCB1 (28%) and 4 RCB2 (36%). Treatment was tolerated well. There were no grade 3 or 4 toxicities. One patient had minor infusion related reaction and grade 2 acne, and 2 grade 2 diarrhea. Conclusions: Neoadjuvant zanidatamab demonstrates significant preliminary efficacy, (pCR/RCB-1 64%) with a good safety profile in patients with stage I node negative HER2+ BC. An update of efficacy and safety of all patients will be presented at the time of meeting Citation Format: Vicente Valero, Jason Mouabbi, Heather Alonzo, Paula Pohlmann, Adaeze Lheme, Amy Hassan, Rashmi Murthy, Xuelin Huang, Wei Qiao, Miral Patel, Gaiane Rauch, Cristina Checka, W. Fraser Symmans, Kelly Hunt, Debu Tripathy, Funda Meric-Bernstam. Neoadjuvant zanidatamab for stage I node negative 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 PS09-03.

Abstract PO5-17-04: Tolerability of pertuzumab in older adults with HER2 positive breast cancer: A single institution experience

Abstract Background: Tumor HER2 over-expression occurs in 10 to 15% of older adults with breast cancer (BC). Combination HER2-directed therapy (pertuzumab and trastuzumab) with chemotherapy (CT) is the standard treatment for early and advanced HER2-positive bc. However, a study of more than 1,300 Medicare beneficiaries showed that about half of patients (pts) aged 65 or older with stage I to III HER2 positive bc did not receive trastuzumab-based therapy. This is likely due to concern for tolerability as older women remain underrepresented in clinical trials of breast cancer making it difficult to extrapolate tolerability of these agents in these patients. In the Neosphere and TRYPHAENA studies, the mean age of pts were 49.8 and 50.6 years, respectively. We examined the real-world tolerability of pertuzumab in combination with trastuzumab and systemic ct in women over the age of 65 with HER2 positive bc. Methods: An IRB approved retrospective review of medical records was conducted evaluating pts over the age of 65 with early or advanced HER2 positive bc treated at The Ohio State University Comprehensive Cancer center from January 1, 2015 to May,1 2020. Descriptive statistics (means, standard deviations, medians and ranges for continuous variables and frequencies and percents for categorical variables) were used to summarize disease and patient characteristics for pts enrolled in this study and treated with pertuzumab. The total number of planned and completed cycles of treatment as well as the number of treatment delays and dose reductions were also summarized using frequencies and percentages. The same descriptive statistics were used to summarize the number of grade II or IV toxicities and pathologic complete response (pCR) in the neoadjuvant setting. Results: A total of 71 pts met inclusion criteria. Mean age was 76 years (SD 4.1). Of these pts, 62 had stage I-III disease and 9 had metastatic disease. Additionally, 68% (48/71) had estrogen positive (ER) disease whereas 32% (23/71) had ER negative disease. Neoadjuvant systemic therapy was provided to 81% (50/62) of non-metastatic pts and 19% (12/62) received adjuvant therapy. The median number of completed neoadjuvant cycles (ct plus trastuzumab and pertuzumab) was 5.4 (SD 1.5). Among those who received pertuzumab with systemic ct in the neoadjuvant setting, 46% (23/50) of pts achieved a pCR (56% for ER negative disease and 41% for ER positive disease) The median number of completed adjuvant cycles (ct plus trastuzumab and pertuzumab) was 4.9 (SD 2.0). Pts with stage I to III disease completed a mean of 8.6 (SD 5.0) targeted therapy cycles (pertuzumab/trastuzumab). Pts with metastatic disease had a median of 5.7 (SD 1.0) cycles of ct plus trastuzumab and pertuzumab and received a mean of 34.4 (SD 36.0) cycles of maintenance pertuzumab. Treatment delay by 7 or more days occurred in 11% (8/71) of pts whereas 25% (18/71) of pts discontinued pertuzumab early. Pertuzumab termination occurred due to toxicity in 44% (8/18), metastasis in 11% (2/18), and other causes in 44% (8/18) of cases. For toxicities, 2% (1/51) of patients reported grade 3 pain, 25% (2/8) reported grade 3 fatigue, and 12% reported grade 4 diarrhea (1/8) (Table 1). Conclusions: Our study showed that pertuzumab was well tolerated in older pts with bc in the real-world setting. However, 25 % of pts still discontinued pertuzumab early which illustrates the importance of identifying pts who are at higher risk for toxicities prior to starting treatment. Table 1 Reported adverse events in patients age 65 and older receiving pertuzumab Citation Format: Nicole Williams, Austin Warmbier, Dureti Doto, Marilly Palettas, Julie Stephens, Dionisia Quiroga, Kai Johnson, Ashley Pariser, Mathew Cherian, Sagar Sardesai, Daniel Stover, Margaret Gatti-Mays, Robert Wesolowski, Bhuvana Ramaswamy. Tolerability of pertuzumab in older adults with HER2 positive breast cancer: A single institution experience [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 PO5-17-04.

Effect of breast cancer prognostic factors on ovarian reserve and response in fertility preservation

Research questionDo breast cancer prognostic factors influence ovarian reserve and response to ovarian stimulation in the context of fertility preservation? DesignObservational, bicentric retrospective study of 352 women with breast cancer who underwent ovarian stimulation using a random start gonadotrophin releasing hormone antagonist protocol and vitrified oocytes between November 2015 and August 2022. Serum anti-Müllerian hormone (AMH) levels and antral follicle count (AFC) were measured. The number of oocytes recovered, maturation rate and follicular output rate (FORT) were analysed according to patients’ characteristics and breast cancer prognostic factors. ResultsMedian age was 34 years (31.1–37.1). Median AFC and serum AMH level were 17 (12–26) follicles and 2 (1.2–3.4) ng/ml, respectively. After ovarian stimulation, 10.5 (6.0–16.0) oocytes were recovered, with eight (4–13) being mature. Mean oocyte maturation rate was 79% (62–92). Antral follicle count (>12) significantly affected the risk of recovering fewer than eight mature oocytes (P < 0.0001, multivariate analysis). Follicular responsiveness to FSH, assessed by the follicular output rate (FORT index) and number of oocytes recovered, were 31% (21–50) and 10.5% (6.0–16.0), respectively. FORT index and ovarian stimulation outcomes were not influenced by breast cancer prognostic factors. ConclusionBreast cancer prognostic factors do not influence ovarian reserve markers or response to ovarian stimulation in fertility preservation. Therefore, tumour grade, triple-negative status, HER2 overexpression and high Ki67 should not alter the fertility-preservation strategy when considering ovarian stimulation for oocyte vitrification.

HER2-low and Overexpression in Mucinous Ovarian Cancer: Analysis of ASCO/CAP and ToGA Immunohistochemical Scoring.

Mucinous ovarian carcinoma is an uncommon malignancy characterized by resistance to chemotherapy and poor survival in the metastatic setting. HER2 amplification is a frequent late event in carcinogenesis, yet the incidence of HER2-low in mucinous ovarian carcinoma is unknown. Further, the optimal method for determining overexpression in these tumors is not established. We sought to assess the ASCO/CAP and ToGA trial scoring methods for HER2 IHC with correlation to FISH, p53, and mismatch repair protein status and to determine the incidence of HER2-low in mucinous ovarian carcinoma. A total of 29 tumors from 23 patients were included. Immunohistochemistry for HER2, p53, MLH1, PMS2, MSH2, and MSH6 was performed. Scoring was performed according to the ASCO/CAP and ToGA trial criteria. HER2 FISH was performed and scored according to the ASCO/CAP criteria. The proportion of HER2-low, defined as 1+ or 2+ staining with negative FISH, was determined. Using ASCO/CAP, 26% demonstrated 3+ while 35% demonstrated 2+ staining. Using ToGA, 30% demonstrated 3+ while 57% demonstrated 2+ staining. By FISH, 26% were positive for HER2 amplification. Both systems captured all FISH-positive cases; the use of ASCO/CAP resulted in fewer equivocal and false-positive cases. Among HER2-negative cases, 88% were HER2-low. Aberrant p53 expression was detected in 55% of cases; mismatch repair deficiency was not identified in any cases. ASCO/CAP guidelines are accurate and resource-effective in determining HER2 overexpression in mucinous ovarian carcinoma. HER2-low is common in these tumors; further studies to determine the role of HER2-targeted therapy including antibody-drug conjugates are indicated.

Varlitinib and Paclitaxel for EGFR/HER2 Co-expressing Advanced Gastric Cancer: A Multicenter Phase Ib/II Study (K-MASTER-13).

Varlitinib is a pan-human epidermal growth factor receptor (HER) inhibitor targeting epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), and HER4. We present a phase Ib/II study of a combination of varlitinib and weekly paclitaxel as a second-line treatment for patients with EGFR/HER2 co-expressing advanced gastric cancer (AGC). Patients whose tumors with EGFR and HER2 overexpression by immunohistochemistry (≥ 1+) were enrolled. Varlitinib and paclitaxel were investigated every 4 weeks. After determining the recommended phase II dose (RP2D) in phase Ib, a phase II study was conducted to evaluate the antitumor activity. RP2D was treated with a combination of varlitinib (300 mg twice daily) and paclitaxel. Among 27 patients treated with RP2D, the median progression-free survival and overall survival (OS) were 3.3 months (95% confidence interval [CI], 1.7 to 4.9) and 7.9 months (95% CI, 5.0 to 10.8), respectively, with a median follow-up of 15.7 months. Among 16 patients with measurable disease, the objective response rate (ORR) and disease control rate were 31% and 88%, respectively. Patients with strong HER2 expression (n=8) had a higher ORR and longer OS, whereas those with strong EGFR expression (n=3) had poorer outcomes. The most common adverse events (AEs) of any grade were neutropenia (52%), diarrhea (27%), aspartate aminotransferase/alanine transaminase elevation (22%), and nausea (19%). No treatment-related deaths or unexpected AEs resulting from treatment cessation were observed in patients with RP2D. A combination of varlitinib and paclitaxel displayed manageable toxicity and modest antitumor activity in patients with EGFR/HER2 co-expressing AGC who progressed after first-line chemotherapy.

HER2 Overexpression in Periampullary Tumors According to Anatomical and Histological Classification-A Systematic Review.

Pancreatic cancer is one of the most aggressive, heterogeneous, and fatal types of human cancer; therefore, more effective therapeutic drugs are urgently needed. Human epidermal growth factor receptor 2 (HER2) overexpression and amplification have been identified as a cornerstone in this pathology. The aim of this review is to identify HER2 membrane overexpression in relation to pancreatic cancer pathways that can be used in order to develop a targeted therapy. After searching the keywords, 174 articles were found during a time span of 10 years, between 2013 and 2023, but only twelve scientific papers were qualified for this investigation. The new era of biomolecular research found a significant relationship between HER2 overexpression and pancreatic cancer cells in 25-30% of cases. The variables are dependent on tumor-derived cells, with differences in receptor overexpression between PDAC (pancreatic ductal adenocarcinoma), BTC (biliary tract cancer), ampullary carcinoma, and PNETs (pancreatic neuroendocrine tumors). HER2 overexpression is frequently encountered in human pancreatic carcinoma cell lines, and the ERBB family is one of the targets in the near future of therapy, with good results in phase I, II, and III studies evaluating downregulation and tumor downstaging, respectively.

Plasmacytoid urothelial carcinoma of the urinary bladder–A clinicopathological and molecular analysis of 52 cases

Plasmacytoid urothelial carcinoma (UC) is a rare histologic subtype of bladder cancer that is associated with an aggressive clinical behavior. We analyzed the clinicopathologic and molecular features of plasmacytoid UC in 52 patients from a single institute. The patients included 44 men and 8 women, with a mean age of 64 years (range, 41–91 years). All bladder cancers were high-grade UC, and plasmacytoid component accounted for a mean of 47% of bladder tumors (range, 5–100%). Distinct gene mutations were found in most plasmacytoid UCs (n = 49); the most common mutations were TP53 (n = 30), followed by TERT (n = 20), and CDH1 (n = 18). Copy number analysis was performed in 34 patients, and 13 of them showed copy number variations. Expression of HER2 was analyzed in 18 patients by immunohistochemistry, and 3 of them showed HER2 overexpression, which was confirmed by fluorescence in situ hybridization analysis. Thirty-two patients died of disease in a median of 15 months (range, 1–45 months). No individual gene mutations were significantly associated with clinical outcome, but mutations in the mammalian target of rapamycin (mTOR) pathway, including PICK3CA and PIK3R1 mutations, were associated with a significantly shorter survival duration (p < 0.05). Plasmacytoid UC is an aggressive histologic subtype that demonstrates frequent somatic gene mutations and CNVs, which may underlie its oncogenesis and progression. Gene mutations of the mTOR pathway are associated with poor outcome in a subset of patients with plasmacytoid UC.