Flow Cytometry and In Vitro Tritiated Thymidine Labeling in Normal Rectal Mucosa of Patients at High Risk of Colorectal Cancer

Objectives : To compare two different methods to evaluate rectal epithelial cell proliferation as a hio-marker of risk of developing colon cancer. Methods : Samples of normal rectal mucosa from 26 patients at increased risk for colorectal cancer (22 patients with adenoma, three with adenocarcinoma ofthe large bowel, and one with longstanding ulcerative colitis) were ex-amined by means of in vitro labeling with tritiated thymidine and flow cytometry. Results : We found a signiHcant correlation between thymidine-labeling in-dex and the percentage of cells in S-phase, measured by flow cytometry both in formalin-fixed, paraffin-em-bedded specimens and in frozen specimens (respec-tively, r= 0.7647, p < 0.001, and r = 0.4503, p < 0.01). However, using flow cytometry, the percentage of cells in S-phase was significantly higher than the thymidine-labeling index in both fixed-embedded and frozen spec-imens ip < 0.01). ProHferative parameters were not higher in patients with colon carcinoma, and were not related to the degree of dysplasia, the number of ade-nomas, or familial occurrence of colorectal cancer. Two specimens taken from normal rectal mucosa of two patients with adenomas showed aneuploidy. No aneu-ploidy was found in normal rectal specimens of patients with adenocarcinoma. Conclusions: These results show that the calculation of cells in S-phase with in vitro tritiated thymidine labeling or by flow cytometry pro-duces different results. However, the significant corre-lation between corresponding parameters obtained with these techniques support the use of either method as "Intermediate biomarkers" of colorectal cancer risk and prognosis.