SUMMARY: ColoRectal Cancer (CRC) is the third most common cancer diagnosed in both men and women in the United States. The American Cancer Society estimates that approximately 140,250 new cases of CRC will be diagnosed in the United States in 2018 and about 50,630 patients are expected to die of the disease. The lifetime risk of developing CRC is about 1 in 21 (4.7%).
Even though the incidence of Colorectal cancer (CRC) in the United States has been rapidly declining overall, primarily driven by screening, the incidence however has been increasing among adults younger than age 50 years. Currently, genetic testing is recommended in patients with polyposis phenotypes, strong family histories, and those whose tumors demonstrate MicroSatellite Instability (MSI) or fail to stain for MisMatch Repair (MMR) gene proteins by immunohistochemistry. Whether patients younger than 50 years of age with CRC, should be tested with a broad multigene panel to detect additional genetic abnormalities, has remained unclear.
The authors conducted this study to ascertain the proportion of young CRC cases associated with genetic predisposition. In this retrospective study, 430 individuals diagnosed with CRC at an age younger than 50 years were evaluated by the clinical genetics service at a single tertiary care cancer center from 1998 through 2015. Data collection included patient histories, tumor phenotypes, and results of germline DNA sequencing. If information was uninformative, germline DNA samples were resequenced using a research-based Next-Generation Sequencing multigene panel. The primary outcome was identification of a pathogenic germline mutation associated with cancer predisposition.
The researchers noted that 26% of young CRC cases had a first-degree relative with CRC and 10% had tumors with histologic evidence for MisMatch Repair (MMR) deficiency and 6% had polyposis phenotype. Germline mutations associated with a hereditary cancer syndrome were identified in 79 patients (18%) following clinically driven germline sequencing, and Next-Generation Sequence analysis using a multigene panel detected actionable germline variants in 6 patients (5%) with uninformative clinical evaluations. Lynch syndrome was identified in 56 patients (14%) of the entire cohort, Familial Adenomatous Polyposis in 2%, MUTYH in 2%, and SMAD4 was mutated in 2 patients, BRCA1 in one, TP53 in one, and CHEK2 in one. Only 51% of the patients with germline mutations associated with a hereditary cancer syndrome gave a family history of CRC diagnosis in a first-degree relative.
The authors concluded that 20% of patients diagnosed with CRC at age younger than 50 years carry a germline mutation associated with cancer, and half of these patients do not have clinical histories typically associated with the identified syndrome. Germline testing with Next-Generation Sequencing multigene cancer panels should therefore be considered for all young patients with CRC. Germline Genetic Features of Young Individuals with Colorectal Cancer. Stoffel EM, Koeppe E, Everett J, et al. Gastroenterology 2017 Nov 13; [e-pub]. (http://dx.doi.org/10.1053/j.gastro.2017.11.004)
