CHEK2 and breast cancer: Other highly penetrant but rare genes include PTEN, TP53, CDH1, and STK11. Moderate penetrance genes, which increase the risk for breast cancer by twofold, include genes involved in DNA repair such as ATM, BRIP1 (BACH1), CHEK2, and PALB2. Still other genes are considered to confer a low but significant risk for breast cancers (Walsh et al., 2017).