The specimen is composed of edematous polyps of varying size that are covered partly by respiratory epithelium and partly by stratified squamous epithelium. Sections show round to spindle-shaped cells with highly variable nuclear size and staining intensity filling the stroma beneath the epithelium. Some of these cells have a moderate amount of eosinophilic refractile cytoplasm. Mitoses are frequent and sometimes abnormal. The cellular infiltrate has widely varying cell density and appears to push against the basal layer of the epithelium. There is a mild mixed inflammatory infiltrate admixed with this proliferating cell population. There are very large and atypical nuclei greater than three times the diameter of their neighbors. A few mutinucleated tumor cells are seen. The immunostain for desmin is strongly positive in almost all of the tumor cells. Pancytokeratin is negative except in the overlying epithelium, and the S-100 stain marks occasional cells scattered within the tumor. Electron microscopic study shows that many cells contain parallel thick and thin filaments, and some tumor cells contain well organized sarcomeres with Z-bands and organized myofilaments.