Rat tumors following fractionated irradiation

Background: Rats are susceptible to irradiation and can develop benign and malignant tumors either spontaneously or in the field of irradiation. In th e head and neck region, them are no reports available on the type of tumor after fractionated irradiation using a human therapy protocol. Material and methods: We analyzed 19 tumors, in 19 rats, which developed after external X-irradiation of the left neck area in Wistar ruts (2 Gy/day, monofraction s, 5 days/week, total dosage 60 Gy) and compared the findings with tumors i n untreated rats of the same strain. Results: Tumors in the irradiation fie ld proved to be squamous cell carcinoma or adenoid cystic carcinoma (ACC) n ot sarcoma. These entities were sporadically found in nonirradiated rats at a higher age. Conclusions:ACC has rarely been reported in the literature o n laboratory rats. The development of this highly aggressive malignant tumo r can be expected 3 months to I year after completion of irradiation.