The effect of trastuzumab-based chemotherapy in small node-negative HER2-positive breast cancer

The prognosis of patients with stage II–III Human Epidermal growth factor Receptor 2 (HER2)-positive breast cancer has significantly improved since the addition of trastuzumab to (neo-)adjuvant chemotherapy. Several reports have shown that small (≤2 cm), node-negative, HER2-positive tumors have a relatively poor prognosis and these patients increasingly receive trastuzumab-based chemotherapy. We aimed to provide evidence for this approach in a population-based cohort. All T1N0M0 HER2-positive breast cancer patients diagnosed between 2006 and 2012 were identified from the Netherlands Cancer Registry. Patient, tumor, and treatment characteristics were recorded. Kaplan–Meier statistics were used for overall survival (OS) and breast cancer-specific survival (BCSS) estimations overall and in T1a, T1b, and T1c tumors separately. Cox regression analyses were performed to account for imbalances in baseline characteristics between treated and untreated patients. A total of 3512 patients were identified: 385 with T1a, 800 with T1b, and 2327 with T1c tumors. Forty-five percent of patients received chemotherapy and/or trastuzumab: 92 % received both. Chemotherapy and/or trastuzumab significantly improved 8-year OS (95 vs. 84 %; hazard ratio [HR] 0.29; 95 % confidence interval [CI] 0.21–0.41, P < 0.001). The effect remained significant in multivariable analyses (HR 0.35; 95 % CI 0.23–0.52, P < 0.001). BCSS was also improved with systemic treatment in univariable (96 vs. 92 %; HR 0.41; 95 % CI 0.27–0.63, P < 0.001) and multivariable analyses (HR 0.31; 95 % CI 0.19–0.53, P < 0.001). Treatment effect on OS and BCSS was similar in T1a, T1b, and T1c tumors. Chemotherapy and/or trastuzumab improves OS and BCSS and can be considered in all patients with small node-negative HER2-positive breast cancer.