Reproducibility of [3H]-Thymidine Labeling Index Determinations in Rectal Mucosal Crypt Organ Culture

This chapter examines a series of laboratory investigations to validate the reproducibility of the [³H]-thymidine labeling index in crypt organ culture of rectal mucosal cells obtained from normal subjects and patients with resected colorectal adenomas and cancers. To demonstrate the reproducibility of the labeling index, a Pearson correlation coefficient was calculated as a measure of association between repeat measurements. Additionally, the mean differences between repeat measurements were calculated to demonstrate that the same level of labeling index was achieved on repeated determinations. While the reproducibility of the labeling index will have to be investigated over a longer timeframe to ensure its relative stability, the data are reassuring with respect to the usual treatment period selected for phase II chemopreventive agent studies. Additional studies to evaluate the effect of various enema and cathartic preparations on the stability of such intermediate markers, including [³H]-thymidine labeling indices, are needed before credence can be given to the results of phase II-type chemopreventive agent studies.