Cell Proliferation and Carcinogenesis in the Hamster Cheek Pouch

Summary Tumors were induced in the cheek pouches of Syrian hamsters of three strains by the topical application of 9,10-dimethyl-1,2-benzanthracene. Mean tumor latent periods and growth rates were determined and tumor cell transit times were measured by tritiated thymidine labeling. Transit times were also measured in untreated cheek pouch epithelium of newborn and adult hamsters and during carcinogen-induced hyperplasia. Within each strain there were qualitative correlations between the mean tumor latent period and the subsequent growth rate of the tumors which developed. Significant differences in the mean latent periods and growth rates of tumors in the different strains of hamsters were observed. Interstrain comparisons indicated that the rate of tumor growth depended more on the existence of a “growth-fraction” and on other factors than on tumor cell transit times. There were indications that nongrowing cells could be divided into two groups: ( a ) cells with a permanent proliferative incapacity, and ( b ) nongrowing cells capable of resuming proliferative activity.