Supplementary Material for: Retrospective study of treatment patterns and natural history of patients with T1a/b N0 TNBCs—A single-institution experience.

Introduction: T1a/b, node-negative (node-), triple-negative breast cancers (TNBCs) are underrepresented in randomized drug-approving clinical trials. Given their low incidence, the clinicopathological features, natural history, and treatment patterns of these tumors remain insufficiently understood. Methods: We conducted a single-institution retrospective cohort study of patients with T1a/b, N0, M0 TNBCs. Deidentified patient- and tumor-related data were collected and summarized. Kruskal-Wallis, chi-square, or Fisher exact tests were used to evaluate associations of interest. Kaplan-Meier methods, log-rank tests, and Cox's proportional hazards models were applied for survival analyses. Results: Of 108 cases of node- TNBCs measuring ≤2 cm, 34 node- T1a/b tumors were included in our analysis. All cases had an intermediate to high histological grade, and most had a Ki-67 score of ≥20%. All patients received adjuvant chemotherapy, and many underwent mastectomy (47%). Docetaxel combined with cyclophosphamide was the most common adjuvant chemotherapy regimen (75%). We did not observe significant associations between improved outcomes and treatment with anthracycline-containing regimens. Among patients with node- pT1a/b tumors, the estimated 3-year recurrence-free survival and distant recurrence-free survival rates were both 96.3% (95% CI, 76.5-99.5), and the overall survival rate was estimated to be 100% (95% CI, 100-100). There were no cases of local recurrences observed. Discussion/Conclusions: In our cohort, all patients with T1a/b node- TNBCs were treated with adjuvant chemotherapy and had favorable outcomes even when treated with anthracycline-sparing regimens.