CHEK2 and breast cancer: In the literature, BRCA1 and BRCA2 are found in approximately 10%-20% of patients with early-onset breast cancer and approximately 13% of patients with early-onset CRC have a hereditary cancer (most commonly Lynch syndrome: 8%).40,41 Additionally, although not seen in the current study, germline mutation of CHEK2 has been associated with both breast and CRC.20,42 In clinical practice, early-onset of either disease should lead to genetic testing.