Colorectal adenomas in young patients: microsatellite instability is not a useful marker to detect new cases of Lynch syndrome.

Purpose: Original Bethesda Guidelines proposed microsatellite instability analysis in colorectal adenomas from patients younger than aged 40 years to identify new cases of Lynch syndrome. We intended to evaluate the characteristics of colorectal adenomas from patients younger than aged 40 years to determine their microsatellite instability status and to correlate it with germline mutations in MLH1 and MSH2 genes.

Methods: Seventy-two adenomas from 58 patients were analyzed. Family history of colorectal cancer, location, and histology of adenomas were evaluated. Microsatellite instability testing was performed with BAT26 only or with the complete Bethesda panel. Germline mutational analysis was performed in MLH1 and MSH2 genes.

Results: Thirty-five patients had a family history of colorectal cancer and 16 of them belonged to Amsterdam Criteria positive families. The remaining 23 presented with sporadic adenomas. Microsatellite instability was found in seven adenomas from seven different patients, all belonging to Amsterdam Criteria-positive families. In six of these patients, a pathogenic germline mutation was identified.

Conclusions: Adenomas diagnosed before aged 40 years presented microsatellite instability only in patients from families with clinical criteria for Lynch syndrome. According to our results, to detect new cases of Lynch syndrome, family history is more important than microsatellite instability testing in adenomas from young patients.