A Case of Cutaneous Smooth Muscle Tumor of Uncertain Malignant Potential

Smooth muscle tumors have been classified into leiomyoma and leiomyosarcoma. But the criteria for malignancy are not well defined. Traditionally, mitoses are the most important differentiating feature between leiomyoma and leiomyosarcoma. However mitotic activity was regarded as an acceptable finding in about 20% of cutaneous leiomyoma. The widely used designation “smooth muscle tumor of uncertain malignant potential” is a reflection of the limitation of available criteria to precisely diagnose tumors with borderline atypical features. We present herein a case of a cutaneous smooth muscle tumor of uncertain malignant potential, which is mitotically active, on the abdomen of a 45-year-old man. (Korean J Dermatol 2008;46(5):678∼681)