Malignant tumor formation in dogs previously irradiated for acanthomatous epulis.

In this retrospective study of 57 dogs irradiated for oral acanthomatous epulis, 2 (3.5%) dogs developed a second tumor (sarcoma, osteosarcoma) in the radiation treatment field at 5.2 and 8.7 years after the end of radiation therapy. As opposed to previous reports, no second epithelial tumors developed in the radiation treatment field. There is a risk of radiation-induced carcinogenesis, but it appears that it is a relatively low risk and an event that occurs years after radiation therapy. Radiation-induced tumors are of more concern in younger dogs that undergo radiation therapy for tumors that are radioresponsive, such as acanthomatous epulis, where long-term survival is expected. The only statistically significant variable in the survival analysis was age, with dogs less than 8.3 years old having a significantly longer median overall survival (2322 days) than dogs older than 8.3 years (1106 days; P<0.0001).