Are we overtreating stage I triple-negative breast cancer in Ontario? A population-based retrospective epidemiological analysis using the ICES database.

Triple-negative breast cancer (TNBC) is associated with inferior outcomes. The use of adjuvant chemotherapy is the mainstay of treatment, and its efficacy was demonstrated to be correlated with tumor size. Different guidelines exist regarding chemotherapy in early-stage TNBC. This study uses ICES database to examine the outcomes of the use of adjuvant chemotherapy in stage I TNBC in Ontario stratified by tumor size. Records of TNBC patients diagnosed in 2012 to 2014 were collected from ICES database. Stage I patients were analyzed by tumor size: T1a (≤ 0.5 cm), T1b (> 0.5 cm and ≤ 1.0 cm), and T1c (> 1.0 cm and ≤ 2.0 cm). Kaplan-Meier curves, log-rank test statistic, and Cox's proportional hazard regression were used to compare differences in overall survival (OS) between chemotherapy and no-chemotherapy groups. Of 610 patients, 183 had tumor sizes ≤ 1 cm, representing stages T1aN0M0 and T1bN0M0, and 427 had tumors > 1 cm to 2 cm, representing stage T1cN0M0. Patients with tumors ≤ 1 cm who received chemotherapy did not have a significant difference in OS compared to the no-chemotherapy group (p = 0.41, hazard ratio (HR) 0.40, 95% confidence interval (CI) 0.021-2.5). However, patients with tumor sizes > 1 cm to 2 cm who received chemotherapy demonstrated significantly better OS compared to those without (p = 0.023, HR = 0.40, 95% CI 0.16-0.86). Patients with TNBC stage T1cN0M0 should receive adjuvant chemotherapy. For TNBC tumors ≤ 1 cm, avoidance of chemotherapy can be considered. Prospective research should further investigate the efficacy of chemotherapy in TNBC stages T1a-bN0M0.Trial Registration University of Windsor REB#16-119.