ERBB2 and breast carcinoma: However, most of these trials consistently excluded patients with tumors that were 1 cm or smaller (pT1mic, pT1a, pT1b), even if different reviews of the literature [11,12,13] and retrospective studies [14,15] evaluating the natural history of small breast cancer based on biological characteristics, showed that HER2+ tumors smaller than 1cm have a worse prognosis than their HER2- counterparts.