Our understanding of subsequent BCs and contralateral BCs is evolving, and data show that females with a PV in BRCA1, BRCA2, PALB2, TP53, or the CHEK2 1100del PV have a high risk of a subsequent and/or contralateral BCs in particular, if their first BC was diagnosed at a young age [1, 3, 22–24]. This evidence concerns the gene CHEK2 and breast cancer.