Abstract P3-05-23: Pathological complete response rate and disease-free survival after neoadjuvant chemotherapy in patients with HER2-low and HER2-0 breast cancers

Abstract

Abstract ABSTRACT Background: Half of HER2-negative breast cancers (BC) show HER2-low expression. The strong efficacy of recent anti-HER2 antibody-drug conjugates (ADC) in HER2-low tumors has risen the interest of HER2-low as a proper BC subtype. Chemosensitivity and prognosis of this subtype are not clear when compared to HER2-0 tumors. We investigated the pathological complete response (pCR) and disease-free survival (DFS) rates in BC patients receiving neoadjuvant chemotherapy for HER2-low or HER2-0 tumors. Methods: Data were collected from the Institut Paoli-Calmettes European Comprehensive Cancer Center database. HER2-low tumors were defined by HER2 IHC score of 1+ or 2+ with negative FISH, and HER2-0 by IHC score of 0+. Clinicopathological characteristics, pCR (defined as [ypT0/ypTis] and [pN0sn or ypN0]) and DFS rates were compared between the two cohorts. Results: From Jan/2005 to Jun/2021, 1,111 patients receiving neoadjuvant chemotherapy were evaluable. The incidence of HER2-low was 41%, including 63% of hormone receptor (HR)-positive and 37% of HR-negative tumors (p< 0.001). In the whole population, the pCR rate was lower in HER2-low (23%) versus HER2-0 (30%) tumors (p=0.013), but this association was lost in multivariate analysis. In HR-positive patients, HER2-low negatively impacted pCR rates when compared to HER2-0 (10% vs. 16%, p=0.046), but not in HR-negatives (46% vs. 42%), and this result was maintained in multivariate analysis (OR 0.60 [95CI 0.36-1.00]; p=0.049, and OR 1.15 [95CI 0.77-1.71]; p=0.490, respectively. No correlation existed between DFS and HER2-status. Conclusion: HER2-low is associated with HR positivity. HER2 status did not impact pCR in HR-negative patients, whereas HER2-low was associated with lower pCR rate in HR-positive patients, supporting the development of anti-HER2 ADC in this setting. Citation Format: Alexandre de Nonneville, Gilles HOUVENAEGHEL, Monique Cohen, Laura SABIANI, Marie BANNIER, Frederic VIRET, Anthony Gonçalves, François BERTUCCI. Pathological complete response rate and disease-free survival after neoadjuvant chemotherapy in patients with HER2-low and HER2-0 breast cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-23.