Myxoid leiomyosarcoma of the uterus: a clinicopathological and immunohistochemical study of 10 cases

Uterine myxoid leiomyosarcoma (MLMS) is a rare tumor that requires modified diagnostic criteria compared with conventional leiomyosarcoma. We analyzed the clinicopathological and immunohistochemical features of 10 MLMS cases from a single institution. Nine of 10 MLMSs showed an invasive border, and 2 of 10 had vascular invasion. Seven cases exhibited low-grade nuclear features, low mitotic counts (median, 2/10 high-power fields), and no tumor cell necrosis. They were all at International Federation of Gynecology and Obstetrics stage I. Two recurred at the vaginal vault at 38 and 61 months, respectively. In contrast, 3 MLMSs with high-grade nuclei had a high mitotic rate (median, 12/10 high-power fields) and tumor cell necrosis (2/3). They were at an advanced International Federation of Gynecology and Obstetrics stage (IIIA-IVB). One had lung metastases at 6 months, and another died at 34 months. HMGA2 immunostaining was diffusely expressed in all MLMSs. Overexpression of p16 and IMP3 was present in 5 and 3 cases, respectively. We conclude that an invasive tumor border and p16 and/or IMP3 overexpression are helpful features in the diagnosis of MLMS. HMGA2 is a highly sensitive and useful marker for MLMS. MLMS might have 2 possible subtypes: high-grade, clinically aggressive MLMS and low-grade, relatively indolent tumors.