Report of an unusual problematic uterine smooth muscle neoplasm, emphasizing the prognostic importance of coagulative tumor cell necrosis.

Follow-up data of the clinical behavior of uterine smooth muscle tumors with low malignant potential are scarce. We present a woman suffering from a uterine smooth muscle cell tumor with increased cellularity, absence of significant atypia, and two to three mitotic figures per 10 HPFs but with minimal focal coagulative tumor cell necrosis (CTCN). These microscopic features are currently accepted to label the lesion as a "smooth muscle neoplasm of low malignant potential, limited experience." After a disease-free survival of 4 years, two retroperitoneal tumors around the iliac vessels were extirpated. Both tumors consisted of smooth muscle cells with mild to moderate atypia and a mitotic index of 5-10 per 10 HPFs but with multifocal and extensive CTCN. These microscopic features were sufficient to establish the diagnosis of leiomyosarcoma. This case adds to the limited experience of the clinical behavior of problematic uterine smooth muscle cell neoplasms and underscores the prognostic importance of CTCN.