Adjuvant Chemotherapy in Lymph Node-Negative, T1 Triple-Negative Breast Cancer

The role of adjuvant chemotherapy in small, node-negative triple-negative breast cancer (TNBC) has not been formally assessed in clinical trials. We aimed to evaluate the benefit of adjuvant chemotherapy in this population.

This is a retrospective study using the National Cancer Database (NCDB). We included women with pathologic T1N0M0 (pT1N0M0) TNBC diagnosed between 2010 and 2019. Kaplan-Meier methods and Cox proportional models were used to compare overall survival (OS) between chemotherapy and no chemotherapy cohorts.

In patients with pT1N0M0 TNBC, adjuvant chemotherapy improved OS (HR, 0.51; 95% CI, 0.47-0.55). The benefit of adjuvant chemotherapy was evidenced across all tumor sizes; T1a HR 0.51 (95% CI 0.34-0.75), T1b HR 0.55 (95% CI 0.47-0.64), and T1c HR 0.48 (95% CI 0.43-0.53). Despite similar HRs associated with chemotherapy across tumor sizes, T1c had the worst OS without chemotherapy, thus the most gain in 5-year OS: 5-year OS rates for chemotherapy vs. no chemotherapy for T1a, T1b and T1c tumors were 98% vs. 93%, 96% vs. 89%, and 93% vs. 80%, respectively. Although there were no ethnoracial differences in chemotherapy receipt, Non-Hispanic Black women (HR 0.65, 95% CI 0.54-0.76) derived less benefit compared to Non-Hispanic White women (HR 0.49, 95% CI 0.44-0.53).

Adjuvant chemotherapy improves survival in patients with pT1N0M0 TNBC. The magnitude of the benefit is greatest for T1c tumors than for T1b and T1a tumors. Future studies are required to identify biomarkers to select patients who derive the most chemotherapy benefit.