Clonogenic, stem and carcinogen-target cells in small intestine.

The small intestine is an epithelial site which rarely undergoes carcinogenic transformation in spite of the fact that it is one of the most rapidly replacing tissues of the body. Some possible explanations for the low cancer incidence are discussed, with particular reference to the target cell population within the epithelium which is capable of carcinogenic transformation. It is proposed that the carcinogen target cells are the stem cells of the tissue and a possible defect which might lead to cancer is a slight alteration in the self-maintenance/differentiation probabilities in favour of self-maintenance.