The role of chronic acanthosis and subacute inflammation in tumor promotion in CD-1 mice by petroleum middle distillates.

An initiation-promotion bioassay using CD-1 mice was conducted to examine the role of chronic acanthosis and inflammation in tumor promotion by petroleum middle distillates (MD). Test groups were initiated with 7,12-dimethylbenz[a]anthracene (DMBA). Promotion with MD consisted of twice weekly treatments for 25 weeks with either 25 or 50 microliters, 50 microliters + daily treatment with 15 micrograms dexamethasone, 50 microliters + postapplication washings, or 100 microliters. Three mice from each group were euthanized at 21-day intervals (24 total per group). The skin from interim euthanized mice was examined histopathologically for tumors, acanthosis, and subacute inflammation. Tumor incidence at study termination was as follows: 25 microliters (45%), 50 microliters (43%), 50 microliters + dexamethasone (0%), 50 microliters + washing (70%), and 100 microliters (81%). A correlation of greater than 0.93 was observed at all intervals between tumor incidence and cumulative group mean degrees of acanthosis in interim euthanized mice. The correlation between subacute inflammation at early through midstudy interval weeks and tumor incidence at study termination was poor. These results support the hypothesis that induction of a lasting, albeit mild, hyperplasia is an essential, but not sufficient requirement for tumor promotion. Furthermore, subacute inflammation does not appear to be a significant factor in tumor promotion by petroleum MD.