Histochemistry of epithelial metaplasia and dysplasia in human stomach and colorectum.

Histochemical techniques reveal the functional divergence of carcinomas of the gastrointestinal tract and their tissues of origin. The principal changes are either the impairment or loss of normal functions or the acquisition of new functions. The latter may be those of heterologous adult tissues (metaplasia) or foetal tissues. Dysplasia or intra-epithelial neoplasia is regarded as a selective precancerous lesion. One might predict the functional profiles of dysplasia to be intermediate between those of normal and carcinomatous tissues. This appears to be only partially true in that high grade dysplasia (amounting to carcinoma-in-situ) will show appropriate cancer-associated changes, whereas low grade dysplasia may be functionally identical to its normal counterpart. Paradoxically, it is possible to demonstrate cancer-associated changes in non-neoplastic lesions such as incomplete intestinal metaplasia of gastric mucosa and both metaplastic polyps and transitional mucosa of the colorectum. If a proportion of the changes occurring in the course of malignant transformation have a metaplastic basis, it is possible that these are caused by the same environmental agents which lead to benign metaplasias. Benign metaplastic lesions may signal the presence of a potentially carcinogenic microenvironment, whilst some, such as incomplete intestinal metaplasia, are regarded as precancerous.