Changes in cell cycle characteristics in hamster cheek pouch epithelium during treatment with DMBA

Cell cycle characteristics were studied in hamster cheek pouch epithelium under normal conditions, in hyperplasia induced by topical DMBA treatment for 5 weeks, in pre‐neoplastic epithelium after 12 weeks of DMBA, and in DMBA induced squamous cell carcinoma. Vinblastine sulphate was used to measure mitotic rate, and the other cell cycle parameters were obtained from tritiated thymidine autoradiography, using the pulse chase method. Te was found to be reduced from the normal value of 163.9 hours to 90.8 hours in hyperplastic epithelium, 22.7 hours in pre‐neoplastic epithelium and 15.4 hours in carcinoma. All phases of the cell cycle were reduced in duration progressively during the stages of carcinoma induction, but the great reduction in Te, was due chiefly to shortening of Tg1 by about 95 %.