[Radiation therapy for the treatment of macroscopic canine anal gland tumors - a retrospective study].

Introduction: Canine anal gland tumors are locally invasive and early metastasize to the loco-regional pelvic lymph nodes. Radiation therapy is a good method for loco-regional tumor control, especially in inoperable tumors. Since the organs in the pelvic area are sensitive to both acute and late radiation damage (chronic diarrhea, bleeding, strictures or intestinal perforations) and such damage mainly depends on the fraction size, we examined the radiation protocol used in this study with a reduced number of fractions (hypofractionated) regarding effectiveness and side effects. This retrospective study describes 13 dogs with macroscopic anal gland carcinoma that were irradiated with imaging-guided, intensity-modulated radiation therapy with a hypofractionated curative protocol of 12 × 3,8 Gy. Gross pathology was either in the region of the anal gland and/or in the sublumbar lymph nodes. Ten of the 13 dogs had advanced tumor diseases (stage 3a or 3b). The acute radiation reactions were mild to moderate and had been reported for some of the dogs in a previous study. The mean study time was 572 days (range 105-1292 days). Disease progression was observed or suspected in 7/13 dogs during the study period: local or loco-regional progression occurred in 3 dogs (23 %) and distant metastases in 4 dogs (31 %). Median progression-free survival was 480 days (95 %CI, 223-908), median survival was 597 days (95 %CI, 401-908). One year after treatment, 76,9 % (95 %CI, 53,5-100) of the dogs were still alive. The likelihood of tumor progression was lower with increasing age, otherwise none of the examined tumor or patient factors showed a prognostic influence on progression or survival time. No clinically relevant late side effects were observed apart from slight alopecia, pigmentation changes or dry, scaly skin, Medium to long-term tumor control can be expected in dogs with macroscopic anal gland tumors treated with a moderately hypofractionated radiation therapy protocol (12 × 3,8 Gy). During long-term monitoring no serious side effects or side effects requiring treatment were observed.