Impact of adjuvant endocrine therapy on prognosis in small hormone receptor-positive, HER2-negative early breast cancer

Background The efficacy of adjuvant endocrine therapy for hormone receptor-positive breast cancer has been previously established. However, significant adverse events related to endocrine therapy cannot be ignored. T1 breast cancer is expected to have a good prognosis. Therefore, adjuvant endocrine therapy for T1a breast cancer patients is controversial. Thus, in this study, we examined the effect of endocrine therapy on the prognosis of T1N0 hormone receptor-positive, HER2-negative breast cancer patients in each tumor size group, and re-considered the application of endocrine therapy. Methods We retrospectively obtained clinical and pathological data from medical records of 7635 patients who underwent surgery for breast cancer at Aichi Cancer Hospital between January 2000 and December 2017. The primary end point of our analysis was disease-free survival (DFS). The secondary end points were distant disease-free survival (DDFS), overall survival (OS), and breast cancer-specific survival (BCSS). The log-rank test, cumulative survival generated curves with Kaplan–Meier methods and the hazard ratio (HR) calculated with a Cox regression model were used to assess the effects of endocrine therapy on prognosis. Results The 5-year DFS was worse in the non-endocrine therapy (non-ET) group (78%) than the endocrine therapy (ET) group (95%) in the T1c population ( p < 0.001, HR 0.25). However, there was no statistically significant difference in DFS between the ET and the non-ET groups in T1a (ET 96% vs non-ET 93%, p = 0.9314, HR 0.94) and T1b (ET 96% vs non-ET 93%, p = 0.1481HR 0.53) breast cancer. The OS, DDFS, and BCSS of the patients also showed that endocrine therapy was associated with improvement of the prognosis in the T1c group, but not in the T1a and T1b groups. Conclusions Adjuvant endocrine therapy may be essential for T1c breast cancer patients. In contrast, this therapy should be discussed for T1a and T1b luminal breast cancer patients under some circumstances, such as suffering from adverse events.