Sebaceous neoplasms in Muir-Torre syndrome.

A 59-year-old Japanese woman presented with two sebaceous neoplasms on the chest wall and on the left cheek. The patient had a history of ascending colon cancer, and her mother had died of gastric cancer. The histopathologic features of both sebaceous neoplasms were vaguely in accordance with those of sebaceous adenoma and sebaceoma. Based on these findings, we diagnosed the patient as having Muir-Torre syndrome. The sebaceous neoplasm on the chest wall exhibited features of a sebaceous adenoma with a unique cystic appearance, namely cystic sebaceous adenoma, which has been reported as a specific marker for Muir-Torre syndrome (MTS). However, histopathologically, both the sebaceous adenoma and sebaceoma had relatively large, vesicular or heterochromous and crowded nuclei with some pleomorphism and distinct nucleoli associated with some mitotic figures, casting doubt on their benignancy. We show that some or most benign sebaceous neoplasms in MTS might have a high potential for malignant transformation or may be well-differentiated sebaceous carcinomas with low-grade malignancy, mimicking sebaceous adenoma/sebaceoma. This results in difficulties in classification regarding sebaceous neoplasms in MTS.