Malignant myopericytoma: expanding the spectrum of tumours with myopericytic differentiation

Aims: The spectrum of tumours showing myopericytic differentiation is increasingly being defined and includes lesions such as myofibroma and infantile haemangiopericytoma. Here we seek to describe for the first time and clinicopathologically characterize examples of malignant myopericytoma. Methods and results: Five cases of malignant myopericytoma were identified in the authors' consultation files. Immunostains were performed and clinical information was obtained. Tumours arose in three females and two males (median age 67 years, range 19–81 years) on the neck, arm, thigh and foot. One patient presented with disseminated metastases. One patient had a prior history of multiple benign myopericytomas in the same location. Four patients developed metastases and three died within 1 year. Tumours were composed of highly mitotic myoid‐appearing ovoid‐to‐spindle cells showing at least focally striking perivascular orientation resembling that seen in benign myopericytoma; three cases were focally fascicular and three showed thin‐walled branching vessels. All tumours showed at least focally prominent positivity for smooth muscle actin. One case showed dot‐like desmin positivity. Conclusions: In reporting examples of malignant myopericytoma, we further characterize and broaden the morphological spectrum of myopericytic neoplasms. Available data indicate that malignant myopericytomas are associated with aggressive clinical behaviour.