CHEK2 and Li-Fraumeni syndrome: Loss of CHEK2 function has been documented in breast cancer (1, 2) colon cancer, renal cell carcinoma (RCC), prostate cancer, ovarian cancer, and some cases of Li-Fraumeni syndrome (3, 4), a familial syndrome more commonly associated with the tumor suppressor gene p53. Patients with Li-Fraumeni syndrome are at risk for breast cancer, soft tissue sarcomas, and adrenal cortical carcinoma (ACC).