Clinical and molecular characterization of colorectal cancer in young Moroccan patients

Early-onset colorectal cancers are relatively rare. About 20% of colorectal cancers are familial or hereditary. Two autosomal dominantly inherited cancer syndromes are more studied: Lynch syndrome accounts for 2-5% of colorectal cancers and familial adenomatous polyposis represents 1% of total colorectal cancers. Unlike the familial adenomatous polyposis syndrome, there are no clinical features that help in easily recognizing Lynch syndrome. The young age of cancer occurrence could be a criterion that should raise a suspicion of Lynch syndrome. In Morocco, the average age at diagnosis of colorectal cancers according to the register of cancers of Casablanca is 56 years, which is 10 years earlier than in European countries. Our study aimed to assess the frequency and molecular characteristics of the Lynch syndrome in Moroccan early-onset colorectal cancers patients.

The population analyzed included 70 patients. The criteria for inclusion of patients in this study were a colorectal cancers before age 50 and the exclusion of familial adenomatous polyposis. We started by searching for microsatellite instability, first by immunohistochemistry of 3 mismatch repair proteins (MLH1, MSH2 and MSH6) and with second confirmation using 4 monomorphic markers (BAT25, BAT26, NR21, and CAT25).

We found instability in 10/70 (15%) of the cases. The loss of expression affects more often the MLH1 protein, with 8 cases, versus 2 cases of altered MSH2. None of the 70 patients of the series fulfilled the Amsterdam II criteria, indicative of Lynch syndrome.

Further work needs to be done to discriminate hereditary cases from sporadic ones, but testing for microsatellite instability as a first step is important.