CHEK2 and breast cancer: Indeed, a recent analysis showed that CHK2 variants found to be dysfunctional in mammalian cell-based assays (found in 0.5% of individuals with breast cancer) were associated with an increased risk of breast cancer, while functionally normal or mildly dysfunctional variants (found in 2.2% of individuals with breast cancer) were not associated with a clinically relevant increased risk of cancer.68