Completion of Genetic Testing and Incidence of Pathogenic Germline Mutation among Patients with Early-Onset Colorectal Cancer: A Single Institution Analysis

Simple Summary Rates of early-onset colorectal cancer (eoCRC), defined as <50 years of age at diagnosis, have increased. Nearly one-quarter of cases of eoCRC may be associated with a germline pathogenic variant (PGV) resulting in a hereditary cancer syndrome. In the present study, we reviewed patients with a history of colorectal cancer who were referred to medical genetics at our institution to better understand the prevalence and spectrum of PGVs in both patients with eoCRC as well as with average-onset CRC (aoCRC). We found that approximately one in four patients with eoCRC had a PGV, which included 8.3% with Lynch syndrome. In patients with aoCRC, similar rates of detection of PGVs were seen. In both groups, approximately one-third of patients referred to medical genetics did not undergo genetic testing. This study reinforces the importance for patients with CRC to undergo genetic testing, especially those with eoCRC. Over the past 20 years, rates of early-onset colorectal cancer (eoCRC), defined as <50 years of age at diagnosis, have increased, with 16-25% associated with a pathogenic germline variant (PGV) resulting in a hereditary cancer syndrome. In the present study, we sought to further characterize PGVs observed in patients with eoCRC. We conducted a retrospective analysis of patients with a history of CRC referred for genetic counseling at Mayo Clinic Rochester between April 2019 and April 2022. Three hundred and three CRC patients were referred to medical genetics, including 124 with a history of eoCRC. Only 84 patients (68%) with eoCRC referred for genetic counseling completed genetic testing, with an average of 48 genes evaluated. PGVs were identified in 27.4% with eoCRC, including 8.3% with Lynch syndrome (LS). Other detected PGVs known to increase the risk of CRC included MUTYH (4.8%), CHEK2 (3.6%), APC, BMPR1A, and TP53 (1.3% each). Among those with aoCRC, 109 patients (61%) completed genetic testing, among which 88% had either a dMMR tumor, personal history of an additional LS malignancy, or family history of LS malignancy, with PGVs detected in 23% of patients. This study reinforces the importance for all patients with CRC, especially those with eoCRC, to undergo germline testing.