Benefit of adjuvant chemotherapy in patients with T1a-bN0, triple-negative breast cancer - A systematic review and meta-analysis

BACKGROUND: The benefit of adjuvant chemotherapy for patients with small, early-stage (T1a-bN0) triple-negative breast cancer (TNBC) is unclear because these patients have largely been excluded from randomized trials. We performed a systematic review and meta-analysis to analyze the effect of adjuvant chemotherapy in this population.

METHODS: We included interventional and observational studies comparing adjuvant chemotherapy with no chemotherapy in patients with T1a-bN0 TNBC. Studies were identified through systematic searches of Medline (PubMed), Embase, and CENTRAL, most recently updated on August 18, 2025. Hazard ratios (HRs) for overall survival (OS) were extracted for meta-analysis. Additionally, 5-year OS and distant recurrence-free survival (DRFS) rates were pooled for patients receiving chemotherapy versus not receiving chemotherapy.

RESULTS: Eighteen non-randomized studies involving 16933 patients were included: 4679 patients received chemotherapy and 12254 did not. Meta-analysis showed significantly improved OS with chemotherapy (HR 0.63, 95 % confidence Interval (CI) 0.43-0.92). Subgroup analyses indicated that the OS benefit was mostly driven by patients with T1bN0 tumors (>5 mm and ≤10 mm) (HR 0.51, 95 % CI 0.34-0.76). In contrast, no OS benefit was observed in patients with T1aN0 tumors (≤5 mm) (HR 1.24, 95 % CI 0.23-6.61). Among all patients with T1a-bN0 TNBC, 5-year OS was 95.9 % with chemotherapy versus 92.0 % without, and 5-year DRFS was 96.0 % versus 92.2 %, respectively.

CONCLUSION: Chemotherapy was associated with higher survival in patients with T1bN0 TNBC, but not in patients with T1aN0 tumors. Overall, 5-year outcomes were high even without chemotherapy. These findings support current guideline recommendations.