Myopericytoma of skin and soft tissues: clinicopathologic and immunohistochemical study of 54 cases.

Perivascular neoplasms comprise traditionally glomus tumor and hemangiopericytoma (HPC). Whereas glomus tumor represents a well-defined entity, the existence of HPC as a separate entity has been questioned because a number of neoplasms of different lines of differentiation are characterized by a HPC-like vascular growth pattern. Myopericytoma represents a recently delineated entity showing a HPC-like vascular pattern. A large series of myopericytoma of skin and soft tissues has been analyzed to further characterize the clinicopathologic spectrum of this entity. Fifty-four cases of myopericytoma of skin and soft tissues were retrieved and the histology reviewed. Immunohistochemical stainings using alpha-smooth muscle actin (ASMA), desmin, and h-caldesmon antibodies were performed, and clinical data and follow-up information were obtained from referring pathologists. Thirty-four patients were male and 18 were female (gender was unknown in 2 cases). Patient age ranged from 13 to 87 years (median, 52 years). The lower extremities were most commonly affected (26 cases) followed by the upper extremities (16 cases), the head and neck region (4 cases), and the trunk (2 cases); exact location was unknown in 5 cases. In 20 cases, the neoplasms were confined to the dermis, in 6 cases an extension into the subcutis was seen, and 24 as well as 4 cases arose in subcutaneous and deep soft tissue, respectively. Two cases were multicentric; and in 1 of these patients, multiple anatomic regions were involved. Histologically, in all cases, numerous thin-walled vessels and a concentric, perivascular arrangement of ovoid, plump spindled to round myoid tumor cells was seen. However, a broad morphologic spectrum ranging from hypocellular, fibroma-like (3 cases), myofibroma-like (2 cases), angioleiomyoma-like (12 cases), and HPC-like neoplasms (13 cases) to classic myopericytomas (14 cases) and immature, cellular lesions (2 cases) was noted. In addition, 2 neoplasms with focal glomoid features, 5 intravascular, and 1 malignant myopericytomas were found. Prominent cytologic atypia and increased proliferative activity (>3 mitoses/10 high power fields) was seen in 4 and 2 cases, respectively. Immunohistochemically, all cases tested stained positively for ASMA. In addition, 29 of 32 cases tested stained positively for h-caldesmon, whereas desmin was only focally positive in 3 of 33 cases. Follow-up information was available in 46 cases (range, 7-168 months; median, 48 months). Despite marginal or incomplete excision in 23 of 46 cases, only 2 neoplasms (1 malignant and 1 intravascular myopericytoma) recurred locally (within 1 and 4 years, respectively). Despite overlapping morphologic features to angioleiomyoma and myofibroma, myopericytoma represents a distinct perivascular, myoid neoplasm of skin and soft tissues, characterized by a broad morphologic spectrum of concentrically, perivascularly growing myoid tumor cells that stain positively for ASMA and often for h-caldesmon, whereas desmin is usually negative. Most cases of myopericytoma behave in a benign fashion, but local recurrences and rarely metastases may occur in atypical and malignant neoplasms.