Colorectal cancer (CRC) occurs rarely in young individuals (<45 yr) and represents one of the criteria for suspecting hereditary cancer families. In this study we evaluated clinical features and molecular pathways (chromosomal instability [CIN] and microsatellite instability [MSI]) in early-onset CRC of 71 patients.
Detailed family and personal history were obtained for each patient. Expression of APC, beta-catenin, p53, MLH1, MSH2, and MSH6 genes was evaluated by immunohistochemistry. MSI analysis was performed and constitutional main mutations of the mismatch repair (MMR) genes were searched by gene sequencing.
Fourteen (19.7%) out of the 71 cases showed both MSI and altered expression of MMR proteins. In the 57 MSI-negative (MSI-) lesions altered expression of APC, beta-catenin, and p53 genes were found more frequently than in MSI-positive(MSI+) tumors. Seven (50%) out of the 14 patients with MSI+ tumors presented clinical features of Lynch syndrome (hereditary non-polyposis colorectal cancer [HNPCC]) and in all but one, constitutional mutations in MLH1 or MSH2 genes could be detected. The same mutations were also found in other family members.
Our study demonstrates the involvement of CIN in a majority of early-onset colorectal tumors. Furthermore, we identified Lynch syndromes in seven cases (50%) of early-onset colorectal carcinomas with impairment of the MMR system. These results suggest that patients with early-onset CRC should be screened for hereditary cancer syndrome through clinical and molecular characterizations.