Intermediate and fine filaments of vascular leiomyomas (angiomyoma), leiomyoma and leiomyosarcomas of large veins.

The expression of fine and intermediate filaments in 10 cases of leiomyosarcoma originating from a large vein, 9 cases of vascular leiomyoma (angiomyoma) and one case of a leiomyoma originating from the wall of the saphena magna vein was studied immunohistochemically by using 6 different anti-desmin antibodies, one anti-vimentin antibody and 2 antibodies to muscle-specific isoforms of actin. All the benign tumors and all the leiomyosarcomas of a large vein as well as the vein of origin were positively stained for desmin. The staining results obtained using the different anti-desmin antibodies varied considerably, however, and formaldehyde-fixed tissues were apparently inappropriate for some of them. No single anti-desmin antibody produced a positivity in all cases, and the extent and distribution of the positivity varied by being irregular and patchy in the leiomyosarcomas and in the muscle walls of the veins, while the benign tumors generally revealed a more uniform and strong positivity. Antibodies to muscle-specific and smooth muscle-specific actin produced a positive staining in all the benign tumors, as well as all the leiomyosarcomas and the veins from which they originated. A strong and uniform positivity was observed in the benign tumors and muscle walls of the veins, while the positivity in the leiomyosarcomas was more irregular, as it was for desmin. Vimentin was constantly expressed in the benign tumors and in the veins of origin, but only in 5/10 of the leiomyosarcomas. It is concluded from this study that the immunohistochemical demonstration of desmin, utilizing a monoclonal antibody appropriate to the type of fixation used, and muscle specific isoforms of actin, provide strong support to the light-microscopic diagnosis of leiomyosarcoma of venous origin.