Pathological Features and Genesis of Carcinoma

Tumors of the large bowel in humans are of three types—adenocarcinoma, carcinoid, and squamous cell carcinoma. Of these, adenocarcinoma is the most common and can be either the fungating exophytic type or the flat infiltrative type. Opinions vary regarding the histogenesis of 

Madara et al. (1983) evaluated the structural evolution of DMH-in-duced rat intestinal neoplasms using the same criteria that were applied to evaluate human colonic adenocarcinomas. These authors showed that many DMH-induced adenocarcinomas in rats have peripheral foci of adenomatous epithelium associated with them. In addition, the frequency of this association correlates inversely with the depth of invasion. These findings are similar to those seen in humans, which have been used as evidence supporting the adenoma-carcinoma sequence. Thus, when assessed using equivalent criteria, DMH-induced intestinal adenocarcinomas appear to be similar to human colonic adenocarcinomas in their 

The neoplastic lesions in rodents and man are located mainly in the distal colon. 

The colon undergoing neoplastic transformation or predisposed to cancer development shows aberrant cell prolification, i.e., a shift in the zone of DNA synthesis, extension of the proliferative compartment, and increased labelling index. 

Neoplastic lesions, including hyperplasias, dysplasia, adenomatous polyps, and carcinomas are present in rodents and humans. 

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