Abstract PO5-17-12: Impact of HER2-low status on axillary response and surgical management after neoadjuvant chemotherapy in early breast cancer

Abstract

Abstract Background: Breast cancer (BC) with low expression of HER2 (HER2-low) might constitute a group of tumors with unique clinical and biological characteristics. Little is known about axillary downstaging and nodal surgical outcomes in HER2-low BC after neoadjuvant chemotherapy (NACT). The aim of this study was to evaluate axillary response and surgical management of the axilla in HER2-low BC patients submitted to NACT. Methods: In this cross-sectional single center study, we consecutively included all patients diagnosed with early HER2-negative BC between 2017 to 2021 that were treated with NACT. Patients must have biopsy-confirmed stage II-III BC, submitted to breast surgery after NACT. Clinical and pathological response in the axilla, type of axillary surgery, and surgical outcomes data were collected. HER2-low was defined by IHC score 1+, or 2+ ISH non-amplified; HER2-zero was defined by IHC score 0. Pathological response was determined locally. Results: At diagnosis, 291 patients had clinically involved axillary nodes (cN1: 69.4%; cN2: 25.1%; cN3: 5.5%). Among 136 patients eligible for SLN biopsy after NACT, 77 (26.5%) had pathologically negative SLN. Of those submitted to upfront axillary dissection (n=154), 52 (33.7%) had pN0 disease. In total, 129 (44.3%) patients with clinically involved axillary lymph nodes at diagnosis were converted to cN0 after NACT. There was no difference in the rate of axillary downstaging between HER2-low and HER2-zero tumors, 17.8% vs 26.5%, respectively (p=0.0026). 236 patients were submitted to sentinel lymph node biopsy (SLN), of whom 214 (81.4%) with blue dye-only, 40 (15.2%) with radioactive isotope, and 7 (2.7%) with dual tracer. SLN detection failure were reported for 12 patients (0.046%). Mean number of lymph nodes retrieved were 2.7. Most patients had a negative SLN biopsy (180/263; 68.4%), of whom 91 (50.6%) were HER2-low and 89 (49.4%) were HER2-zero. Positive SLN biopsy were reported in 83 patients (isolated tumor cells: 20,5%; micrometastasis: 24.1%; macrometastasis: 55.4%), with capsular extravasation in 25.3%. A positive SLN biopsy occurred in 61.4% of patients with HER2-low tumors, and in 38.5% of patients with HER2-zero tumors. Among patients with a positive SLN biopsy (n=83), 67 were submitted to axillary dissection, of whom 39 (58.2%) had no additional nodes involved (HER2-low: 61.5%; HER2-zero: 38.4%). Considering N0 tumors at diagnosis, 127 patients were submitted to SNL, and only 18.9% had a positive result (HER2-low: 66.6%; HER2-zero: 33.3%). In the subgroup of initially cN+ disease, 136 (46.7%) underwent SLN biopsy, with 59 (43.4%) with a positive result (HER2-low: 59.3%; HER2-zero: 40.7%). Conclusions: Our results showed that HER2-low BC patients had a statistically significant lower frequency of axillary downstaging after NACT. More than 40% of patients with cN+ at diagnosis were downstaged to cN0 and were submitted to SNL biopsy. Axillary dissection were avoided in roughly 25% of patients with cN+ BC at initial staging. Citation Format: Leonardo Roberto da Silva, Guilherme Sartori, Susana Ramalho, Tomás Reinert, Mahira Lopes Da Rosa, Grazielle Morais Tavares, Higor Mantovani, Vivian Vasconcelos, Ana Elisa Ribeiro Da Silva Cabello, Guilherme Coelho, Jovana Mandelli, Facundo Zaffaroni, Carlos Barrios, Marcia Silveira Graudenz, César Cabello. Impact of HER2-low status on axillary response and surgical management after neoadjuvant chemotherapy in early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-17-12.