A young man who had received a diagnosis of advanced colon cancer and liver metastases was recently referred to a genetics service for a molecular analysis, and a mutation in a mismatch repair gene was identified. However, records at the molecular analysis laboratory revealed an even more tragic story. Approximately 20 years previously, the patient’s family had undergone genetic testing following diagnosis of a sebaceous carcinoma in an older relative of the patient and the suspicion of Muir-Torre syndrome, a rare familial disorder. The family underwent an extensive consultation session, followed by blood sampling and a molecular analysis of the sebaceous carcinoma biopsy sample. Although the tumor clearly showed microsatellite instability–high activity, no mutation could be identified using the available technology. The family was advised about the need for regular clinical surveillance, as well as routine follow-up colonoscopy and gynecological examinations.