Low level X-radiation effects on carcinogenesis by 7,12-dimethylbenz(a)anthracene in Syrian hamster cheek pouch epithelium: acute vs fractionated radiation dose studies

Studies examined the effects of acute and fractionated low to moderate level X-ray exposures on hamster cheek pouch carcinogenesis in vivo by 7,12-dimethylbenz(a)anthracene (DMBA). Animals were grouped by treatment as follows: acute doses of 0.85-3.40 Gy X rays; 17 once weekly doses of 0.01-0.20 Gy X rays (fractionated radiation); topical DMBA for 10 weeks; DMBA plus fractionated radiation starting together; DMBA plus acute radiation in Week 1 or 10 of DMBA treatments; and sham irradiation, DMBA vehicle, or anesthesia controls. After 44 weeks, hamsters were sacrificed, and their cheek pouches were excised, serially sectioned, and examined by light microscopy for histopathology. No histologic changes were observed in radiation-only hamsters. Carcinoma incidences in DMBA-only groups ranged from 45 to 60%. Carcinoma incidences were greater in groups receiving DMBA plus fractionated radiation than in groups receiving either acute radiation + DMBA or DMBA alone. Carcinoma incidences in acute radiation plus DMBA groups were lower than those in DMBA-only groups. These results suggest complex interactions between radiation and DMBA, perhaps with radiogenic cell killing being a principal factor in acute radiation + DMBA groups, and reciprocal additive or synergistic effects of radiation and DMBA on cancer induction and manifestation in fractionated radiation + DMBA groups.