The causal implication of many germline variants in Mendelian diseases has long been recognized (http://omim.org/).5 Numerous cancer predisposing germline variants have also been identified in tumor suppressor genes (TP53, RB), in genes involved in DNA repair (e.g., BRCA1, PALB2, MLH1, MSH2/6, CHEK2, and ATM), cell proliferation (e.g., PTEN, STK11, RET, and FGFR) and cell adhesion (e.g., CDH1, APC).6–9 However, only a small proportion of breast cancer risk can be attributed to high penetrance germline mutations, with each individual SNP contributing only marginally to the risk of cancer. This evidence concerns the gene RET and cancer.