Features of colorectal adenomas among young patients with Lynch syndrome according to path_MMR: Results from the PRED-IdF registry.

BACKGROUND: Lynch syndrome (LS) is the most frequent inherited colorectal cancer syndrome. AIM: To assess the burden of adenoma in LS patients under 50 years-old followed in the PRED-IdF network. METHODS: From January 2010 to January 2019, all patients under 50 years of age with a confirmed LS germline mutation were included. The main objective was the description of adenomas characteristics according to path_MMR. RESULTS: We analyzed data from 708 patients (mean age 34.8 ± 8.6), of which 41.8 % were male. Among these patients, 37.6% had path_MLH1, 45.4% path_MSH2, 13.9% path_MSH6, 2.9% path_PMS2, and 1.2% path_EpCAM. The analysis included 1721 (70.9%) follow-up colonoscopies. A total of 682 adenomas were detected, including 140 (20.5%) advanced adenomas. The adenoma detection rates during the first and follow-up colonoscopies were 19.2% and 20.5%, respectively. Most adenomas were <10 mm (57.9%), located in the proximal colon (334, 48.9%), and presented as non-polypoid lesions (493, 72.3%). The median growth time for adenomas was 23 months (range 9-114) irrespective of the path_MMR mutation (p = 0.62). CONCLUSION: LS patients under 50 years of age have a high burden of adenomas, particularly small non-polypoid adenomas located in the proximal colon. These results highlight the need for intensive screening, with a particular focus on the proximal colon.