Survival outcome of weak estrogen/progesterone receptor expression in HER2 negative breast cancer is similar to triple negative breast cancer

Abstract Background Recent publications have suggested that human epidermal growth factor receptor 2 (HER2)-negative breast cancers with “weak” estrogen receptor (ER)/progesterone receptor (PR) expression levels by immunohistochemical (IHC) analysis were considered as the triple-negative (TN) subtype. This study aimed to evaluate the overall survival (OS), disease-free survival rates (DFS), and disease-specific survival (DSS) based on ER and PR expression levels into one of three groups, ER and PR 20% by hormone therapy. Methods Medical records of 3353 breast cancer patients treated from 2006 to 2013 were retrospectively reviewed. Tumor characteristics, type of treatment, OS, DFS and DSS were evaluated among the three patient groups. Results Regarding OS, there were significant differences according to the received hormone therapy in the different groups: ER and PR P  = 0.972), ER and PR 1%–20% ( P  = 0.264), and ER or PR >20% ( P  = 0.014). Regarding DFS and DSS, there were also significant differences in the different groups: ER and PR P  = 0.611, 0.766), ER and PR 1%–20% ( P  = 0.847, 0.629), and ER or PR >20% ( P  = 0.031, 0.002). Conclusions In HER2 negative breast cancer patient with hormone therapy, ER and PR expression level of 1%–20% has similar survival outcome to the ER and PR expression level of