Among the 5953 unselected Polish individuals with cancer in this study, 533 CHEK2 mutation carriers were identified, including 186 probands with breast cancer (9.2% of the total tested) (mean age of diagnosis: 55.6 years; range: 27–82 years), 147 probands with colon cancer (7.6% of total; mean age of diagnosis: 61.9 years; range: 25–88 years) and 200 probands with prostate cancer (10.0% of total; mean age of diagnosis: 65.7 years; range: 45–88 years). The gene discussed is CHEK2; the disease is prostate cancer.