Small HER2-positive breast cancer: which prognosis and which adjuvant treatment?

Incidence of centimetric or infracentimetric node negative (pT1a-b, N0) breast cancer is increasing due to screening procedures. Although considered as having an overall favorable prognosis, several retrospective studies have suggested a higher risk of relapse when HER2 is overexpressed. Since randomized studies evaluating trastuzumab in the adjuvant setting did not include T1a-bN0, there is no level I evidence supporting the administration of a trastuzumab-based post-operative chemotherapy in these cases. However, some recent retrospective data suggest a benefit for such a strategy and current guidelines recommend to consider adjuvant chemotherapy plus trastuzumab in pT1bN0. The final decision, as well as the nature of cytotoxics to be administered in combination with trastuzumab, require a careful evaluation of the benefit/ risk ratio in order to minimize the risk of toxic events, notably at the cardiac level.