Females with BC and cancer of ≥ 1 other site (multiple primary cancers, MPC) who underwent MGPT through Ambry Genetics from March 2012 to December 2016 were included if they had testing of at least 21 genes of interest (ATM, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, EPCAM, MLH1, MSH2, MSH6, MUTYH, NBN, NF1, PALB2, PMS2, PTEN, RAD51C, RAD51D, STK11, and TP53). This evidence concerns the gene CHEK2 and breast cancer.