Among patients with small (pT1mic/a pN0/1mi) HER2+ breast cancers, disease recurrence rate was significantly lower among patients who received adjuvant Trastuzumab (4% Trastuzumab group vs. 26% non-Trastuzumab group, p = 0.02), with this therapy conferring an 85% reduction in the risk of relapse (HR 0.15; 95%CI 0.10–0.97; p-value: 0.048). This evidence concerns the gene ERBB2 and breast cancer.