Immunohistochemical and immunoblotting detection of cytokeratin in smooth muscle tumors.

Forty-six smooth muscle tumors, including 35 of gastrointestinal origin, were studied immunohistochemically for the localization of cytokeratin using a variety of monoclonal antibodies. In formalin-fixed, paraffin-embedded material, six of 40 leiomyomas, two of five leiomyosarcomas and one leiomyoblastoma were immunoreactive for cytokeratin in a few tumor cells. A proportion of non-neoplastic smooth muscle cells also exhibited a positive reaction. In fresh frozen sections of one gastric leiomyosarcoma, a high percentage of tumor cells were reactive with nine of the eleven anti-cytokeratin monoclonal antibodies examined. Cytokeratin-positive cytoplasmic filaments were further demonstrated by immunoelectron microscopy. By immunoblot analysis, an extract of this immunohistochemically cytokeratin-positive leiomyosarcoma showed a distinct band at the same position as an extract of pancreas, whereas no bands were seen in an extract of a cytokeratin-negative esophageal leiomyosarcoma. These immunohistochemical and immunoblotting findings indicate that a certain subset of smooth muscle neoplasms express genuine cytokeratin filaments.