CHEK2 and breast cancer: Group 1 includes likely causal variants, representing genes known to be associated with an increased risk of the given cancer type, e.g. BRCA1 and BRCA2 in breast, ovarian and pancreatic cancer, BAP1 in melanoma and mesothelioma, etc. This group also includes variants with a reduced penetrance, e.g., the CHEK2 c.1100del variant in breast cancer.