Hamster Cheek Pouch Response to Varying Lengths of Carcinogen Exposure

¹ College of Dentistry, University of Kentucky, Lexington, Kentucky
² School of Dentistry University of Pennsylvania, Philadelphia, Pennsylvania

The cheek pouches of adult hamsters were exposed for varied times to an 0.5 per cent mineral oil solution of 7,12-Dimethylbenz () anthracene. Four of thirteen animals exposed to carcinogen by painting for 1 week according to the methods of this experiment developed tumors by 21 weeks. Seven of 13 animals painted 2 weeks developed tumors by 21 weeks. During the course of the experiment four tumors were observed grossly in animals of Group I and three in animals of Group II which could not be found after 21 weeks.

All animals painted according to methods of this experiment, for 3 weeks or more, developed tumors by 21 weeks. All animals painted three weeks developed tumors, however, the latent period was prolonged. Animals painted 4 weeks did not differ from those painted 5-12 weeks in latent period required for tumor development in all animals. The longer animals were painted (up to 8 weeks) the greater was the number of tumors which developed in 21 weeks. The longer animals were painted (up to 9 weeks) the larger was the size of the largest tumor which developed in 21 weeks. Animals which were painted for 10, 11, and 12 weeks revealed after 21 weeks tumors of such number and size that group differences could not be determined. Responses resulting from more than 9 weeks of painting were considered maximum.

All animals painted 1 and 2 weeks revealed a moderate epithelial hyperplasia of the pouch and some disruption of basal cell continuity when observed after 21 weeks. There were no obvious differences in the histology of tumors regardless of the groups in which they appeared. The critical biochemical changes of carcinogenesis have transpired in the mucosa of the hamster cheek pouch which has been exposed to carcinogen tri-weekly for 4 weeks.