Lynch syndrome is a genetic condition associated with tumours of the colon, reproductive organs, and urinary tract. Less commonly, neuro-endocrine tumours have also been reported. We describe the first case of a Lynch syndrome patient presenting with a neuroendocrine lung tumour manifesting as cortisol excess (Cushing’s syndrome) in a middle-aged woman.

In addition to the germline MLH1 splice site mutation, genetic analysis revealed a complete gene deletion of MLH1 as somatic second hit, confirming the tumor’s link to Lynch syndrome. Furthermore, we provide a comprehensive review of the existing literature on neuroendocrine tumors occurring in Lynch syndrome. (By Kevin Van Compernolle, on behalf of co-authors Jacques Van Huysse, Kathleen Claes, Ellen Denayer, Marie Bex, and Annick Van den Bruel, https://jmg.bmj.com/content/early/2025/11/23/jmg-2025-110900 )