A Comparison of the Cell Cycle in Induced Carcinomas and Their Normal Counterpart

Summary The kinetics of cell proliferation of normal basal epithelium and induced epithelial tumors of the hamster pouch were studied in an effort to find differences between normal and tumor cells in a situation where the correspondence of these cells was reasonably assured. The tumors were induced in albino hamsters by painting the pouches with 7,12-dimethylbenz[α]anthracene. Unpainted and tumorous pouches were removed at multiple periods after the intraperitoneal injection of tritiated thymidine. From autoradiographs of fixed tissue sections, various indices of labeling in mitotic and total cells were determined. These indices were used to calculate the mean transit time of the cells through visible mitosis ( T M ), DNA synthesis ( T S ), the post-synthetic gap ( T G2 ), and the entire cycle ( T C ). For normal basal cells the values were T M , 2.6 hours; T S , 10.2 hours; T G2 , 1.6 hours; and T C , 142 hours. For the tumor cells, the corresponding values were T M , 0.4–0.6 hours; T S , 6.1 hours; T G2 , 2.2 hours; and T C , 17.5–20.7 hours. An incomplete analysis of hyperplastic nonmalignant epithelium of the painted pouches suggested that T S was unchanged from the normal, whereas T M and T C were 0.5 and 42 hours, respectively. In spite of the independent origin of each pouch tumor, there appeared to be remarkably little variation between tumors.