Several studies have revealed that variants in familial BC susceptibility genes like BRCA1, BRCA2, TP53, PALB2, CDH1, PTEN (OMIM 601728), PIK3CA (OMIM 171834), STK11 (OMIM 602216), RINT1 (OMIM 610089) and NF1 (OMIM 613113) are not only associated with BC predisposition, but also with a number of other malignancies [7, 9, 23–29]. This evidence concerns the gene PIK3CA and breast cancer.