Mixed adenocarcinoma and carcinoid tumour of the colon. A report of 4 cases with postulates on histogenesis.

Gastro-intestinal tumours which contain both mucinous and endocrine cells have been reported with increasing frequency recently. Four such mixed neoplasms of the colon are described. Macroscopically, the tumours caused muscular hypertrophy resulting in thickening of the wall of the bowel and annular stenosis of the lumen. Microscopic examination showed them to be poorly differentiated adenocarcinomas with a distinct carcinoid component. Both the mucinous and endocrine elements were demonstrated in metastatic deposits of the tumour, so confirming the malignant nature of each component. The neoplasms appear to represent a distinct clinico-pathological entity associated with a poor prognosis. The histogenesis is postulated to be a range of neoplasms from pure adenocarcinoma through mixed tumours to pure carcinoids and small-cell undifferentiated carcinoma. Such mixed tumours could arise from neoplastic change of crypt-base stem cells.