Pathology of Uterine Leiomyosarcomas and Smooth Muscle Tumours of Uncertain Malignant Potential

Uterine leiomyosarcomas are the most common uterine sarcomas. For clinicians, they are difficult tumours to manage. Preoperative detection is difficult because of the similarity in clinical presentation to ordinary fibroids. They are highly aggressive tumours and the effectiveness of adjuvant therapy remains controversial with surgery remaining the mainstay of treatment. Despite treatment, disease frequently recurs. For pathologists, diagnosis of most leiomyosarcomas using current diagnostic criteria is usually straightforward, as most tumours often possess two or more diagnostic microscopic features, including diffuse atypia, high mitotic count and tumour cell necrosis. Diagnostic difficulties usually relate to tumours having only one of these worrisome features, with or without other additional unusual morphologic findings. These latter tumours have been labelled as uterine smooth-muscle tumours of uncertain malignant potential. Those that are followed by a recurrence are biologically low-grade leiomyosarcomas. Epithelioid and myxoid leiomyosarcomas are less common, and their diagnostic criteria are different to tumours of usual spindle cell differentiation. In this review, we discuss the pathology of leiomyosarcomas, including an update on smooth-muscle tumours of uncertain malignant potential, with emphasis on the controversy of labelling of atypical leiomyomas. The problems with histologic diagnosis, immunohistochemical studies and molecular pathology are reviewed.