Tritiated thymidine incorporation into epithelial cells of normal-appearing colorectal mucosa of cancer patients.

A radioautographic analysis of the number and position of labeled epithelial nuclei after in vitro incorporation of tritiated thymidine ([3H]TDR) was carried out with 30 specimens of histologically normal colorectal mucosa from 26 patients, of whom 13 were being treated for rectal or sigmoid cancer and 13 were controls. A higher mean labeling index was found in the cancer than in the control group (9.8% +/- 1.2 and 7.9% +/- 0.9, respectively). Because of wide individual variations, this difference was not statistically significant. However, a highly significant upward shift of the proliferating cell compartment was observed in the cancer group, resulting in a specific modification of the [3H]TDR labeling pattern in 6 of 17 specimens. DNA synthesis predominated in the middle or middle and upper thirds of the crypts of Lieberkühn rather than in the lower third as observed in controls. The patchy alteration of epithelial cell renewal frequently accompanying colorectal cancer was suggestive of a defect in the regulatory control mechanism. This in vitro [3H]TDR incorporation assay could provide a valuable discriminatory parameter in studies of high-risk populations.