This newly acquired evidence that strongly highlights the clinical validity of protein truncating variants in genes beyond BRCA1/2, led to the expansion of these guidelines to include testing of other high-risk breast cancer genes, including CHEK2, CDH1, BRIP1, NF1, PALB2, PTEN, RAD51C, RAD51D, STK11, and TP53 [17,18]. This evidence concerns the gene CHEK2 and breast cancer.