Virchows Arch [Pathol Anat] (1983) 401:57-66 Virchows ArchivA © Springer-Verlag 1983 Undifferentiated carcinoma of the colon containing exocrine, neuroendocrine and squamous cells Ivan Damjanov 1, Peter S. Amenta 1, and Fred T. Bosman 2 1 Department of Pathology and Laboratory Medicine, Hahnemann University School of Medicine, Philadelphia, Pennsylvania 19102, USA, z University of Limburg Medical School, Maastricht, The Netherlands Summary. The light microscopic, electron microscopic and histochemical features of a highly malignant colonic tumor resected from a 39 year old man are presented. The tumor was composed predominantly of un- differentiated cells with focally admixed neuroendocrine, exocrine and squamous cells, occasionally arranged in an organoid manner. Histo- chemically the tumor contained argyrophilic cells as well as cells that reacted positively with the antibodies to alpha-l-antitrypsin, alpha-1- antichymotrypsin, carcinoembryonic antigen and lysozyme. The term "stem cell carcinoma of the intestine" is proposed for this highly malig- nant tumor composed of undifferentiated cells exhibiting only focally their multidirectional developmental capacity. Key words: Keratin Alpha-l-antitrypsin - Lysozyme It has been known for quite some time that gastrointestinal carcinomas may on occasion contain argentaffin or argyrophil cells (Hamperl 1927). In addition to these "carcinomas with included argentaffin or argyrophil cells" (Lillie and Glenner 1960) there are tumors composed of both neuroen- docrine and mucin secreting cells (Heruandez and Reid 1969), neuroendo- crine cell carcinomas containing foci of mucin rich cells (Tahara et al. 1982) and so called amphicrine cell tumors (Ratzenhofer 1977; Ratzenhofer and Auböck 1980). All these observations coupled with experimental data ob- tained from heterotransplantations of human gastrointestinal tumors (Gol- denberg and Fisher 1970) and clonings of rat tumors of the colon (Cox and Pierce 1982) suggest that some gastrointestinal tumors arise from stem cells capable of differentiating into both exocrine and neuroendocrine cells. Other reports (Park and Reid 1980) indicate that the stem cells of some tumors may differentiate not only along the pathways which are normal Offprint requests to: I. Damjanov at the above address