Male breast cancer exhibits a heterogeneity of molecular alterations, basically reflecting those observed inER+/HER2- female breast cancers, including frequent mutations of PIK3CA (20–36%) and of GAT3 (15–16%), but less frequent TP53 mutations (3–7%) than in women breast cancers (Figure 5) [257,258]. The gene discussed is PIK3CA; the disease is breast cancer.