Vascular leiomyosarcoma: Clinicopathology and immunohistochemistry with special reference to a unique smooth muscle phenotype.

Vascular leiomyosarcoma (LMS) is the least frequent type of soft-tissue LMS and has not been fully evaluated immunohistochemically. The aim of the present study was therefore to examine four cases of vascular LMS, paying special attention to the immunohistochemical expression of smooth muscle markers. All the patients were female; two tumors were located within the inferior vena cava, one within the saphenous vein, and one within the external iliac vein. All the tumors displayed well-moderately differentiated smooth muscle morphology. On immunohistochemistry all four vascular LMS were diffusely and strongly reactive to actins, calponin, and h-caldesmon, whereas desmin was diffusely stained in one tumor, only focally positive in two, and negative in one. The walls of the blood vessels contiguous to the tumors contained desmin- and h-caldesmon-positive smooth muscle cells in two cases. In contrast, among 43 non-vascular LMS (20 well-moderately differentiated and 23 poorly differentiated or other types), 38 were variably positive for desmin, whereas 21 were negative for h-caldesmon. These findings suggest that the vascular LMS displays a distinctive phenotype of smooth muscle differentiation according to histopathogenesis.