Benefit of adjuvant chemotherapy for T1cN0M0 and selected T1bN0M0 triple-negative breast cancer: a nationwide cancer registry-based study.

Background: The efficacy of adjuvant chemotherapy for T1N0M0 triple-negative breast cancer (TNBC) has not been clearly elucidated. Thus, we aimed to evaluate the efficacy of adjuvant chemotherapy for patients with T1a-cN0M0 TNBC.

Patients and methods: Patients newly diagnosed with TNBC between 2011 and 2015 were identified and followed up until the end of 2020 using the Taiwan Cancer Registry. Univariate and multivariate Cox proportional hazards regression analyses were performed to compare the recurrence-free survival (RFS) and OS between patients who received and those who did not receive adjuvant chemotherapy.

Results: Of the 62 483 patients registered during 2011-2015, 1074 patients with T1N0M0 TNBC (T1a, n = 103; T1b, n = 167; and T1c, n = 804) who underwent definitive breast surgery were included. Overall, 850 (79%) patients received adjuvant chemotherapy; these comprised 24.3%, 67.7%, and 88.6% of the patients with T1a, T1b, and T1c disease, respectively. Over a median follow-up of 7.18 years, a significant RFS and OS benefit from adjuvant chemotherapy was observed in the T1c subgroup but not in the T1a and T1b subgroups. However, subgroup analysis of T1b disease indicated that adjuvant chemotherapy yielded an OS benefit to patients with histological grade III disease (adjusted hazard ratio = 0.08, 95% CI, 0.01-0.77; P = .03).

Conclusions: Adjuvant chemotherapy improved the RFS and OS in patients with T1cN0M0 TNBC and improved the OS in patients with histological grade III T1bN0M0 disease. Our study advocates for the utilization of adjuvant chemotherapy in patients diagnosed with T1cN0M0 and histological grade III T1bN0M0 TNBC.