Tumors with smooth muscle differentiation.

Background: In the classification of tumors of soft tissue, modern schemes describe tumors by the normal adult tissue type the tumor resembles. Thus, tumors are described as smooth muscle tumors if the cells are differentiating towards smooth muscle. We may infer that in fact the tumor arose from smooth muscle, but this is only an inference. Tumors showing differentiation towards smooth muscle include hamartomas, benign tumors, and malignant tumors.

Objective: This review article describes the clinical presentation and course, histology, and treatment recommendations for benign and malignant smooth muscle tumors.

Methods: An extensive literature review of tumors with differentiation towards smooth muscle.

Results: Benign tumors exhibiting differentiation towards smooth muscle include smooth muscle hamartoma and leiomyoma. Myofibroma is a third tumor that some have argued is a smooth muscle tumor rather than a fibroblastic tumor. Characteristic fusiform shaped cells with a round central nucleus arranged in fasicles suggest smooth muscle differentiation. Special stains such as phosphotungenistic acid-hemotoxilin, analine blue, and Masson's trichrome are helpful in differentiating muscle from collagen. Immunohistochemical stains are also helpful in establishing a diagnosis. With solitary tumors, treatment for cosmesis or for painful leiomyomas is not a problem. Multiple leiomyomas, which may be painful or sensitive to cold or touch, are a therapeutic challenge, with reports of multiple medications being attempted in the literature. Leiomyosarcoma are malignant tumors of smooth muscle. They may be cutaneous and presumably arise from the arrector pilorum muscle, or subcutaneous, where they are believed to arise from vascular smooth muscle. Cutaneous leiomyosarcomas frequently reoccur following excision, but rarely metastasize. Subcutaneous leiomyosarcomas frequently reoccur following excision and have a high metastatic rate. Several recent reports have documented an increased frequency of visceral leiomyosarcomas in immunosuppressed patients. These tumors have been found to contain the Epstein Barr virus. Treatment of leiomyosarcoma is wide excision.

Conclusions: Smooth muscle tumors are rare neoplasms that may confront the dermatologic surgeon. While leiomyomas are benign, their frequent sensitivity or pain necessitates treatment. Leiomyosarcomas are malignancies with a high reoccurrence rate, and when deep, a high metastatic rate. The finding of an increased frequency of visceral leiomyomas and leiomyosarcomas in immunosuppressed patients may imply an increased frequency of cutaneous leiomyomas and leiomyosarcomas in this patient population.