CHEK2 and Familial prostate cancer: Rare MSVs in CHEK2 were also associated with increased risk of both breast and prostate cancer, with RRs of approximately 1.4, comparable to previous estimates for breast cancer,6 25 and to estimates for the association of the I157T variant and prostate cancer.10 40 The RR for breast cancer was higher for variants classified as likely deleterious by Helix score.