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

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-induced neoplasms in Syrian hamster cheek pouch epithelium. Doses employed were 0.05 ml of 0.1% 7,12-dimethylbenz[a]anthracene (DMBA) in mineral oil twice weekly for 10 weeks and 20-R head and neck X radiation once weekly for 17 weeks. Animals received either radiation alone, DMBA alone, or simultaneous radiation + DMBA beginning together. Appropriate controls were performed. Radiation alone did not result in any detectable pathology. In one study, the incidence (68 vs 40%) and volumes of tumors were significantly greater in animals receiving radiation + DMBA than in animals receiving DMBA alone. The latent period for earliest tumor appearance was shorter in animals receiving radiation + DMBA than in animals receiving DMBA alone (9 weeks vs 24 weeks). In the repeat study, increased tumor incidence in the radiation + DMBA group was again observed, but ...