Carcinogenic effects of intragastric 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene in Wistar and Sprague-Dawley rats

In 2 experiments involving 384 rats of the Wistar (W) and Sprague-Dawley (SD) strains, the carcinogenic effects of repeated intragastric instillations of 3-methylcholanthrene (MCA) were compared with those of single intragastric doses of 7,12-dimethylbenz[a]anthracene (DMBA). Mammary carcinomas appeared in a higher proportion and earlier in SD than in W rats exposed to either carcinogen (during 36 weeks, 90 vs. 50% with MCA in SD and W rats, at an average of 12 and 15 weeks, respectively, and 80 vs. 64% with DMBA in SD and W rats, at an average of 16 and 22 weeks, respectively). Fibroadenomas of the breast were seen in 20 percent of SD rats by 36 weeks. In W rats observed for 1 year following DMBA administration, Fibroadenomas occurred in 64 percent and adenosis in 49 percent, at an average of 45 to 51 weeks, whereas after MCA administration these reactions occurred in less than 10 percent. Intraluminal secretion indicative of lactation was noted in approximately 20 percent of fibroadenomas and adenoses. Nine W rats developed lymphoma, 5 following DMBA and 4 following MCA administration. Uterine papillary formations were observed in 1 W and 2 SD rats, and uterine carcinomas in 2 SD rats; 3 animals had received DMBA and 2, MCA.