Even though the results of our study demonstrated that HER2-positive pT1a-bN0M0 breast cancer might have a worse clinical history and the addition of trastuzumab to adjuvant treatment could improve the prognosis of such patients, the real association between different subtypes and survival outcomes as well as the efficacy of trastuzumab offered to HER2-postive patients in pT1a-bN0M0 breast cancer is far from clear. This evidence concerns the gene ERBB2 and breast cancer.