A case of Muir-Torre syndrome with a keratoacanthoma and sebaceous neoplasms: Clinicopathological features and a speculation on the pathogenesis of cutaneous tumor type.

Muir-Torre syndrome is a hereditary condition characterized by occurrence of sebaceous neoplasms or keratoacanthomas and visceral tumors. The most common mechanism for this syndrome is a constitutional defect in the mismatch repair genes. We report the case of a 67-year-old woman with a mutator L homologue 1 (MLH1) mutation. She had a history of endometrial and colorectal cancers. The patient presented with a typical keratoacanthoma on the right cheek and numerous sebaceous neoplasms on the face and trunk. Seven sebaceous adenomas and a low-grade sebaceous carcinoma were excised. Most sebaceous adenomas showed dermoscopic features such as some yellow comedo-like globules and curved vessels in creamy-white areas. Moreover, they revealed pathological features such as keratoacanthoma-like architecture and peritumoral or intratumoral lymphocytes. One of these sebaceous adenomas indicated histopathologically spontaneous regression and another was continuous with the hair follicle. Immunohistochemical staining for mismatch repair proteins revealed loss of expression for MLH1 and postmeiotic segregation increased 2 (PMS2) proteins in tumor cells nuclei in both keratoacanthoma and sebaceous adenoma. Nuclei in overhanging epithelial lips of the keratoacanthoma were also negative. These findings suggest that the type of Muir-Torre syndrome-related cutaneous tumor may have been affected by mismatch repair protein deficient sites in the pilosebaceous unit.