[Mesenchymal uterine tumors. Leiomyomas]

Leiomyomas are by far the most frequent mesenchymal uterine neoplasms. Leiomyoma variants refer to a particular histological differentiation and growth pattern, respectively. To assess malignancy, an algorithm is used based on the presence or absence of cellular atypia, tumor cell necrosis and mitosis. In addition, vascular invasion is a criterion for malignancy. Ischemic or infarct type necrosis is not considered a criterion for malignancy. The differential diagnosis of leiomyosarcoma includes cellular and mitotically active leiomyoma and leiomyoma with extensive infarct type necrosis (apoplectic leiomyoma). The term smooth muscle tumor of uncertain malignant potential (STUMP) should be reserved for tumors with uncertainty regarding cell type, type of necrosis and mitotic index, as well as for special cases of myxoid and epithelioid smooth muscle neoplasms. Immunohistochemically, the expression of desmin and caldesmon is indicative of smooth muscle tumors, while stromal tumors can express smooth muscle actin and, rarely, desmin in addition to CD10.