Methods of treating patients having HER2-positive, locally advanced or previously untreated metastatic breast cancer having received prior treatment with a taxane using an anti-HER2-maytansinoid conjugate (for example trastuzumab emtansine) are provided.L'invention concerne des procédés de traitement de patientes atteintes d'un cancer du sein HER2 positif, de première ligne métastatique ou localement avancé.