HER2-Low Status and Response to Neoadjuvant Chemotherapy in HER2 Negative Early Breast Cancer

Abstract

Purpose: Recently, phase I studies with novel antibody drug conjugates targeting HER2 suggested benefit in HER2-low patients – defined as immunohistochemistry(IHC) +1 or +2 FISH/ISH non-amplified, with advanced breast cancer(BC). Data on the prognostic value of HER2-low in early stage disease is scarce. The purpose of this study was to evaluate the impact of HER2-low status on response to neoadjuvant chemotherapy(NACT) and survival outcomes in early stage HER2- negative BC. Methods: Records from all BC patients treated with NACT from January 2007 to December 2018 in a single cancer center were retrospectively reviewed. Primary objective was to compare differences between pathologic complete response(pCR) and relapse free survival(RFS) in luminal HER2-low/HER2-0 and triple negative(TNBC) HER2-low/HER2-0. Results: 855 non-HER2-positive patients were identified. Median follow-up was 59 months. 542 had luminal BC (63.4%) and 313 TNBC (36.6%). 285 (33.3%) were HER2-low. Among luminal tumors, 145 had HER2 IHC+1 (26.8%) and 91 IHC+2/ISH non-amplified (16.8%). In TNBC, only 36 had HER2 IHC+1 (11.5%) and 13 IHC+2/ISH non-amplified (4.2%). Among luminal/HER2-low and luminal/HER2-0 population, there was a high proportion of clinical T3/4 (61.5% vs 69.2%, p=0.053), node positive (74.2% vs 66.3%, p=0.27) and stage III tumors (63.1% vs 65%, p=0.51). The same was true TNBC/HER-low as compared to TNBC/HER2-0, despite a non-statistically significant higher cT4 among TNBC/HER-low (32.7% vs. 19.3%, p=0.17). pCR was 13% in luminal/HER2-low versus 9.5% in luminal/HER2-0 (p=0.27), and 51% in TNBC/HER2-low versus 47% in TNBC/HER2-0 (p=0.64). 5y RFS was 72.1% in luminal/HER2-low and 71.7% in luminal/HER2-0 (p=0.47), and 75.6% in TNBC/HER2-low versus 70.8% in TNBC/HER2-0 (p=0.23). HER2-low status was not associated with RFS in multivariate analysis (HR 0.83, 95%CI 0.6–1.11, p=0.21). Conclusion: Our data does not support HER2-low as a biologically distinct BC subtype, with no predictive effect on pCR after NACT nor prognostic value on survival outcomes.