Enhancement of DMBA Tumorigenesis in Hamster Cheek Pouch Epithelium by Repeated Exposures to Low-Level X Radiation

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Abstract
Duplicate studies were conducted to determine the effects of repeated exposures to low-level X-radiation on the incidence, volume and latent period of DMBA[7,12-dimethylbenz[a]anthracene]-induced neoplasms in Syrian hamster cheek pouch epithelium. Doses employed were 0.05 ml of 0.1% DMBA in mineral oil twice weekly for 10 wk and 20-R head and neck X-radiation once weekly for 17 wk. Animals received radiation alone, DMBA alone or simultaneous radiation + DMBA beginning together. Appropriate controls were performed. Radiation alone did not result in any detectable pathology. In 1 study, the incidence (68 vs. 40%) and volumes of tumors were significantly greater in animals receiving radiation latent period for earliest tumor appearance was shorter in animals receiving radiation + DMBA than in animals receiving DMBA alone (9 vs 24 wk). In the repeat study, increased tumor incidence in the radiation group was again observed, but without the decrease in tumor latent group was again observed, but without the decrease in tumor latent period. These results are compatible with synergy between low-level X-radiation and DMBA in terms of numbers of animals developing tumors, and also with low-level irradiation altering the biological progression of these DMBA-induced tumors. The results are suggestive of low-level X-radiation acting as a synergistic cocarcinogen.