Mutation spectrum of germline cancer susceptibility genes among unselected Chinese colorectal cancer patients

Background: Genetic factors play an important role in colorectal cancer (CRC) risk, yet the prevalence and spectrum of germline cancer susceptibility gene mutations among unselected Chinese CRC patients is largely undetermined. Methods: We performed next-generation sequencing with a 73-genes panel and analyzed the prevalence and spectrum of germline mutations in 618 unselected Chinese CRC patients. We classified all identified germline alterations for pathogenicity and calculated the frequencies of pathogenic mutations. Clinical characteristics were assessed by age and mutation status. Protein expressions and interactions of MLH1 missense variants were evaluated by western blot and co- immunoprecipitation. Results: Overall, 112 (18.1%) of 618 unselected Chinese CRC patients were found to carry at least one pathogenic or likely pathogenic variant (totaling 97 variants), including 70 (11.3%) Lynch syndrome (LS) mutation carriers and 42 (6.8%) non-LS mutation carriers. LS mutation carriers were significantly younger at CRC diagnosis and were more likely to have right-sided, poorly differentiated, early stage, high-frequency microsatellite instability (MSI-H) or dMMR CRC and a family history of cancer compared with noncarriers. Non-LS mutation carriers were more likely to be proficient mismatch repair (pMMR) than noncarriers (p=0.039). We found four clinical variables (gender, tumor histological stage, cancer stage and mutation status) that showed significant differences between patients younger and older than 50 years old. Higher mutation rates were found in patients under 50 years old (p=0.017). Thirty-three novel variants were discovered and evaluated as pathogenic mutations by our study. Conclusion: Given the high frequency and wide spectrum of mutations, genetic testing with a multigene panel should be considered for all Chinese CRC patients under 50 years old and is also needed to determine whether a gene is associated with CRC susceptibility and to promote clinical translation.