Carcinoma of the colon with undifferentiated, carcinoid, and squamous cell features

An undifferentiated small cell tumor of the colon that was found by light- and electron-microscopic study to possess features of a malignant carcinoid merged into keratinizing squamous cell carcinoma. Single cells contained both dense-core secretory granules and tonofilaments. The implications of this combination in relation to theories of tumor origin and differentiation are briefly discussed.