Muir-Torre syndrome: role of the dermatopathologist in diagnosis.

Muir-Torre syndrome (MTS) is an autosomal dominantly inherited disorder characterized by sebaceous lesions and visceral malignancies. The defect is thought to be the result of a mutation in mismatch repair genes and associated with microsatellite instability. Two cases whose diagnoses were suggested first by the dermatopathologist are discussed. The first is a 47-year-old white man who over the past 6 years developed multiple sebaceous lesions. Due to the number of sebaceous lesions and their morphology, the possible diagnosis of MTS was suggested by the dermatopathologist. Subsequently, a lesion in the right colon was found during colonoscopy that proved to be a poorly differentiated cecal adenocarcinoma. A pedigree analysis revealed other family members afflicted with multiple malignancies. Genetic testing of the colonic adenocarcinoma showed microsatellite instability. The second patient is a 50-year-old white man who underwent biopsy of a skin lesion that showed features of both a sebaceous hyperplasia and sebaceous adenoma. Because of the mixed, unusual features of the lesion, the dermatopathologist suggested the diagnosis of MTS. It was later confirmed that the patient had a history of malignancies of the colon and kidney as well as a family history significant for multiple malignant neoplasms. These cases demonstrate the important role of the dermatopathologist in alerting the clinician to the possibility of Muir-Torre syndrome when the diagnosis of a sebaceous neoplasm is made, especially when unusual histologic features are observed.