Adjuvant chemotherapy in small node-negative triple-negative breast cancer (TNBC).

Abstract

536 Background: International guidelines differ in their recommendation for adjuvant chemotherapy in small node negative TNBC. We evaluated associations of chemotherapy with long-term outcome in a large population-based TNBC cohort. Methods: All patients diagnosed with pT1N0M0 TNBC between 2005 and 2015 were identified from the Netherlands Cancer Registry. Patient, tumor and therapy characteristics were recorded. Date and cause of death were obtained from Statistics Netherlands. We used multivariable cox regression models to evaluate associations of chemotherapy with overall survival (OS) and breast-cancer specific survival (BCSS), adjusted for baseline characteristics. Subgroup analyses were performed by tumor size and grade. Results: We identified 4393 patients: 284 with T1a, 924 with T1b, and 3185 with T1c tumors. Chemotherapy was administered in 53% of patients: 6% with T1a, 17% with T1b and 67% with T1c. Chemotherapy use increased over time and varied by geographic region. Patients receiving chemotherapy were younger, had larger tumors, higher tumor grade, and more often isolated tumor cells (itc) in the lymph nodes. At a median follow-up of 7 years (IQR 5-10 years), 611 patients had died, of whom 287 due to breast cancer. Chemotherapy was associated with improved OS in the whole group (adjusted hazard ratio [aHR] 0.55; 95% CI 0.44–0.69), in the pT1c subgroup (aHR 0.53, 95% CI 0.41-0.67), and in grade 3 tumors (aHR 0.50, 95% CI 0.39-0.65). Associations were not significant for pT1ab or grade 1-2 tumors (table). Findings for BCSS were in line with OS results (table). To illustrate the absolute difference we estimated 10-year OS and BCSS for a 60-year old woman with a pT1cN0(itc+) grade 3 TNBC. The predicted 10-year OS was 67% with chemotherapy and 49% without; predictions for 10-year BCSS were 80% and 66%, respectively. Conclusions: Adjuvant chemotherapy is associated with higher OS and BCSS in small node negative TNBC. Benefit is most evident in grade 3 tumors and tumors > 1cm and not evident in tumors ≤1cm and grade 1-2.[Table: see text]