Cytokeratin-specific monoclonal antibodies are reactive with tumours of smooth muscle derivation. An immunocytochemical and biochemical study using antibodies to intermediate filament cytoskeletal proteins.

Formalin fixed and paraffin wax embedded tissue from 13 leiomyosarcomas, three leiomyoblastomas, five leiomyomas and fresh tissue from one leiomyosarcoma and one leiomyoma was studied. Tumours were stained by the avidin-biotin-peroxidase technique with antibodies to desmin, vimentin, cytokeratins and S-100 protein. Neoplastic cells in all the cases were positive for desmin and vimentin but were negative for S-100; antibody CAM 5.2 gave strong reactivity with tumour cells of 12 leiomyosarcomas and all leiomyomas, but failed to stain the leiomyoblastomas; LP34 weakly stained two leiomyosarcomas and one leiomyoblastoma. Immunoblot studies using whole cell extracts of one leiomyosarcoma and one leiomyoma respectively, showed 55-58 kd and 35-38 kd bands reactive with monoclonal antibody CAM 5.2. However, no cytokeratin components were demonstrated when cytoskeletal extracts of the same tissue samples were immunoblotted with CAM 5.2. The implications of these findings for the diagnostic histopathologist are discussed.