Smooth muscle tumors of soft tissue.

This paper presents an overview of smooth muscle tumors occurring in deep soft tissue. Although the existence of leiomyomas of soft tissue has been questioned in the past, it appears that they do exist but are rare, and must be diagnosed using stringent histologic criteria that include no atypia and minimal or no mitotic activity. They segregate into two distinct clinicopathologic groups, one group occurring in patients of either sex in deep somatic soft tissue and the second occurring primarily in women in the pelvic retroperitoneum. The latter bear a histologic similarity to uterine leiomyomas. Leiomyosarcomas occur in retroperitoneum followed by deep somatic soft tissue and are diagnosed by the presence of nuclear atypia and essentially any level of mitotic activity. Leiomyosarcomas of deep somatic tissue commonly arise from small veins and their behavior can be predicted by a number of factors including age, grade, and "disruption" of tumor. Conversely, few factors have proved to be prognostically useful for leiomyosarcomas of the retroperitoneum, as nearly all prove fatal. Epstein Barr virus (EBV)-associated smooth muscle tumors are a recently emerging entity that occur in the setting of immunocompromise. Their behavior is closely tied to the immune status of the patient rather than to specific histologic features.