Prognosis and Influencing Factors of ER-positive, HER2-low Patients with Residual Diseases after Neoadjuvant Chemotherapy: A Retrospective Study

Background: Previously, we found that estrogen receptor (ER)-positive, HER2-low patients is insensitive to neoadjuvant chemotherapy (NACT). And the outcomes of patients with residual diseases were worse than that of patients who achieved pathological complete response (pCR) after NACT. The purpose of this study is to explore the prognosis and influencing factors of these patients . Methods A total of 618 ER-positive breast cancer patients who received thrice-weekly standard NACT were enrolled, including 411 ER-positive, HER2-low cases. Clinicopathological features before and after NACT of these patients were collected. Univariate and multivariate COX regression analyses were used to find the independent factors of 5-year disease-free survival (DFS). Results Of the ER-positive, HER2-low patients, 49 cases (11.9%) attained pCR after NACT. A significant survival difference was shown in patients with or without residual diseases after NACT. Level changes in immunohistochemical markers and tumor stages before and after NACT were significant. According to univariate and multivariate analyses, we found that significant associations between cN_stage ( P  = 0.002), ER ( P  = 0.002) and Ki67 ( P  = 0.023) expression before NACT with 5-year DFS, while pT_stage ( P  = 0.015), pN_stage ( P  = 0.029), ER ( P  = 0.020) and Ki67 ( P ༜0.001) after NACT was related to 5-year DFS in ER-positive, HER2-low patients with residual diseases. Conclusion Our study suggested that pre- and post-NACT high proliferation, low ER expression level and advanced stage both were associated with poor prognosis, which provides a reference for developing long-term treatment strategies for ER-positive, HER2-low patients with residual diseases in the future.