Tumor size is a relevant prognostic factor for early breast cancer patients and data from US National Cancer Database showed that among 123,212 patients with pT1a-b pN0 breast cancer, unselected for HER2 status, 5-year survival rates were marginally but significantly higher for pT1a than pT1b (94.3% vs 93,1%, p = 0.04) [25]. Here, ERBB2 is linked to breast cancer.