Vascular leiomyosarcoma: the malignant counterpart of vascular leiomyoma.

The clinical and pathological findings of six cases of leiomyosarcoma arising from blood vessels of different caliber are described. The term vascular leiomyosarcoma, having both a topographic and morphologic significance, is proposed for these tumors. The histologic pattern is characterized by a proliferation of atypical smooth muscle cells with a large number of intermingled blood vessels. Mitoses were counted per 10 high power field (hpf) and tumors were divided in three groups I, 10 to 20 mitoses, group II, 20 to 35 mitoses, and group III, more than 35 mitoses per 10 hpf. The mitotic index seems to be the most important pathological feature on which a prognostic evaluation for vascular leiomyosarcoma can be based. Tumors in group I had neither local recurrences nor metastases; the one tumor in group II had one local recurrence, but the patient is free of disease 6 years after surgical treatment; the three tumors in group III developed distant metastases and constitutional symptoms. Vascular leiomyoma, bizarre leiomyoma, and hemangiopericytoma are included in the differential diagnosis of vascular leimyosarcoma. The possibility that vascular leiomyosarcoma arising from small vessels represents the malignant counterpart of vascular leiomyoma is proposed.