New threshold of ER positivity in early stage HER2- breast cancer.

Abstract

1067Background: ASCO/CAP recommends 1% as the cutoff value for ER positivity. However, several studies show that tumors with 1% ≤ ER < 10% behave similarly to those with ER < 1%. Whether ER expression will impact the pCR rate after neoadjuvant chemotherapy (NAC) in HER2- primary breast cancer is unknown. Our primary objective was to determine whether the quantitative ER value is predictive of pCR rate for newly diagnosed HER2- early stage breast cancer treated with NAC. The secondary objectives were to identify the optimal cutoff of ER to stratify patients who are less likely to achieve pCR and to test this cutoff in terms long-term benefits of hormonal therapy. Methods: A total of 3237 patients with early stage HER2- breast cancer were included in analysis. Logistic regression models were used to determine the association between each variable and pCR. Kaplan-Meier curves along with log-rank test and Cox proportional hazard models were used for survival analysis. Martingale residual plots, recursive part...