BG13 A rare case of Muir–Torre syndrome

Abstract

Abstract Muir–Torre syndrome is a rare variant of hereditary nonpolyposis colorectal cancer, also known as Lynch syndrome. It is caused by a defect in mismatch repair genes, which are most commonly inherited in an autosomal dominant fashion. It is characterized clinically by sebaceous neoplasms of the skin associated with at least one visceral malignancy, with colon cancer being the most frequent. The most common genetic defects responsible are in MLH1, MSH2 and MSH6, which results in an increased frequency of unrepaired base mismatching during DNA replication and subsequent microsatellite instability, predisposing to cancer. We present a case of a 59-year-old man with a history of colon cancer who was referred with a rapidly growing irregular nodule on his lower back for the past 2 months, concerning for an amelanocytic melanoma. An excision biopsy was arranged, and subsequent histology demonstrated a sebaceoma. Immunohistochemistry for mismatch repair genes showed loss of expression for MSH2 and MSH6. Upon further questioning, it was found that he had a strong family history of colon cancer (father, brother and two sisters), and he developed colon cancer at 36 years of age, which was treated with a pancolectomy. Genetic testing revealed a mutation in MSH2. Given this history, annual follow-up was arranged for skin surveillance.