In our study using retrospectively collected data from the Japanese BCR held within the NCD, we identified 2736 patients with early-stage pT1N0 HER2+ breast cancer and demonstrated significantly improved survival benefits (DFS: HR 0.45; 95% CI 0.32–0.68 and OS: HR 0.54; 95% CI 0.31–0.94) in those who received systemic treatment in the pT1c group (Table 2). Here, ERBB2 is linked to breast cancer.