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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 the head and neck region, there 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 rats (2 Gy/day, monofractions, 5 days/week, total dosage 60 Gy) and compared the findings with tumors in untreated rats of the same strain.


RESULTS
Tumors in the irradiation field proved to be squamous cell carcinoma or adenoid cystic carcinoma (ACC), not sarcoma. These entities were sporadically found in non-irradiated rats at a higher age.


CONCLUSIONS
ACC has rarely been reported in the literature on laboratory rats. The development of this highly aggressive malignant tumor can be expected 3 months to 1 year after completion of irradiation.