Comparison of suspected Lynch syndrome patients carrying BRCA and BRCA‐like variants with Lynch syndrome probands: Phenotypic characteristics and pedigree analyses

BACKGROUND: Colorectal cancer (CRC) patients diagnosed with Lynch syndrome (LS) are recommended genetic testing. Increasing numbers of germline variants involved in homologous recombination have been identified in suspected LS patients. This study compared phenotypic the characteristics of suspected LS patients carrying BRCA and BRCA‐like variants with those of LS patients. METHODS: Forty‐two patients carrying pathogenic variants of DNA mismatch repair (MMR) genes (MMR group), 9 carrying BRCA variants, and 11 carrying BRCA‐like variants (BRCA/BRCA‐like group) who met LS clinical criteria were enrolled in this study. Clinical characteristics, pedigrees, and survival rates were compared and BRCA variants were analyzed. RESULTS: The earliest CRC‐onset age and tumor differentiation were higher in the BRCA/BRCA‐like group than in the MMR group. Metachronous CRCs were more numerous in the MMR group, resulting in a higher progression‐free survival rate in the BRCA/BRCA‐like group. Extra‐colorectal cancers were more frequently observed in the BRCA/BRCA‐like group. BRCA2 and BRCA1 variants were clustered in exons 11 and 4/7, respectively. CONCLUSION: BRCA and BRCA‐like variants in CRC patients with LS showed moderate penetrance. BRCA/BRCA‐like variant carriers had a higher risk for extra‐colorectal cancers. Surveillance of susceptible organs other than the intestine should be performed for probands and affected family members.