Somatic mutations are a frequent cause of Lynch-like tumors

Vogelaar , Ingrid1

Lynch syndrome is the most frequent cause of hereditary colorectal cancer (CRC) and caused by mutations in the mismatch  repair genes. Inactivation of the MMR system results in microsatellite instability (MSI), which is a hallmark of Lynch syndrome tumors. However, in a subset of patients with an MSI-positive tumor, no genetic explanation for the MMR-deficiency can be found.

In the March issue of Gastroenterology, Arjen Mensenkamp and Ingrid Vogelaar (photo), together with colleagues from the departments of Human Genetics and Pathology of the Radboudumc, report on the occurrence of two somatic events in these tumors explaining the MMR-deficiency in more than 50% of the MMR-deficient tumors without causal germline mutations or promoter methylation. Patients with these tumors no longer need to be considered as Lynch-like and thus the surveillance regimen for these patients and their relatives can be based on their family history. This most often reduces the frequency and starting age of colonoscopies and eliminates the need for surveillance for extracolonic Lynch syndrome-associated tumors.

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