Determination of cocarcinogenic activity of benzo[e]pyrene for respiratory tract mucosa.

As benzo[e]pyrene (B[e]P) has been shown to enhance the carcinogenic effects of benzo[a]pyrene (B[a]P) on mouse skin [26], it therefore seemed important to determine if it would also act as a cocarcinogen in another target tissue, namely respiratory tract mucosa. Tracheal mucosa of rats was concomitantly exposed to B[a]P and B[e]P for up to 6 months. At B[a]P/B[e]P ratios of 1 : 1 and 0.5 : 1, B[e]P had no cocarcinogenic effects on tracheal epithelium. At the higher B[a]P/B[e]P ratio, B[e]P appeared to reduce the carcinoma incidence from 65% (B[a]P alone) to 40% (B[a]P plus B[e]P). In sharp contrast to the carcinoma incidence, the tracheal and peritracheal sarcoma incidence was enhanced 2-3-fold by B[e]P. Thus, while not cocarcinogenic for tracheal epithelium, B[e]P was cocarcinogenic for connective tissue. Together with other results [26], these point to the importance of the target tissue as a determining factor of cocarcinogenic activity of test substances.