Importance: Adjuvant chemotherapy remains the only recommended treatment for patients with triple-negative breast cancer (TNBC). However, the existing evidence is not enough to recommend adjuvant therapies to patients with T1 N0 M0 TNBC.
Objective: To evaluate the association of different adjuvant therapies with survival outcome in patients with T1 N0 M0 TNBC stratified by cancer stage and age.
Design, setting, and participants: Postoperative patients diagnosed as having T1 N0 M0 TNBC between 2010 and 2015 who were enrolled in the Surveillance, Epidemiology, and End Results cancer registry program were included in this population-based cohort study. Data analysis was performed from March 27, 2019, to August 10, 2020.
Exposures: Chemotherapy and radiotherapy.
Main outcomes and measures: Kaplan-Meier curve and univariate and multivariable Cox proportional hazards regression analyses were performed to compare overall survival (OS) and breast cancer-specific survival (BCSS) between the different treatments.
Results: A cohort of 7739 eligible patients (mean [SD] age, 59.5 [12.4] years; all female) were included in the present study. The 5-year OS of the total patients was 91.7% (95% CI, 90.9%-92.5%), and median follow-up was 45 months (95% CI, 44-46 months). Patients aged 70 years and older or with T1a TNBC were more likely to receive adjuvant radiotherapy than chemotherapy. Although any adjuvant therapy could improve OS in T1 N0 M0 TNBC, only chemotherapy was associated with significantly better breast cancer-specific survival (BCSS adjusted hazard ratio: 0.657; 95% CI, 0.460-0.939; P = .02). Adjuvant radiotherapy after breast-conserving surgery was associated with better OS and BCSS in patients aged 70 years and older but not in those younger than 70 years. For patients with T1c BC, chemotherapy after breast-conserving surgery or other surgery was associated with improved OS, whereas only chemotherapy after other surgery was associated with better BCSS.
Conclusions and relevance: The findings of this cohort study suggest that adjuvant therapies could improve OS in patients with T1 N0 M0 TNBC, whereas only chemotherapy was associated with better BCSS. Older patients with early-stage TNBC may benefit from adjuvant radiotherapy. Administration of adjuvant therapies to patients with different ages and cancer stages should be discussed carefully, which necessitates guidance from updated guidelines.