Simple Summary This study evaluates a radiotherapy treatment for anal sac tumors in dogs. The treatment consists of five doses of 4 Gy given consecutively, either alone or combined with other therapies. Our primary objective is to compare the survival and prognostic metrics among patients. Records from fifty dogs were analyzed, showing that those receiving radiotherapy alone (n = 22) had a median survival of 384 days, and a progression free interval of 337 days vs. 628 and 402 days, respectively, from radiotherapy combined with other therapies (n = 28). The treatment caused mild side effects and rare late effects. Overall, adequate palliation for AGASACA can be expected with radiotherapy alone via this dose with acceptable toxicities, and extended survival is possible when combined with other treatments with acceptable toxicities as well.Abstract This research aims to evaluate the outcomes of a radiotherapy protocol, consisting of five fractions of 4 Gy each, resulting in a total dose of 20 Gy for apocrine gland anal sac tumors and local lymph nodes in canines. This protocol was assessed as a palliative treatment for macroscopic tumors alone, or in combination with additional therapies under different scenarios. Medical records from fifty canine patients met the inclusion criteria and were divided into different treatment groups: radiotherapy alone (n = 22, 44%), radiotherapy with chemotherapy or targeted therapy with toceranib (n = 18, 36%), surgery with radiotherapy (n = 5, 10%), and surgery with radiotherapy and chemotherapy or targeted therapy with toceranib (n = 5, 10%). Patients who received radiotherapy alone had a median survival time of 384 days (95% CI 198-569) and 628 days (95% CI 579-676) for RT + additional therapies. The median time to progression for patients with radiotherapy alone was 337 days (95% CI 282-391 days), and 402 days (95% CI 286-517 days) for radiotherapy plus additional treatments. Acute side effects were mild, with the majority having diarrhea (61%), and only one patient developed grade III late effects VRTOG v2 classification; however, this happened 22 months after the first radiotherapy protocol after re-irradiation. The results demonstrate that radiotherapy alone under this protocol provided a comparable median time to progression vs. radiotherapy plus additional treatments while maintaining acceptable side effects. The combination of this protocol with other treatment modalities offers attractive results for local disease control and survival while maintaining acceptable toxicities. Overall, these findings contribute to the growing evidence supporting the role of radiotherapy in managing apocrine gland anal sac adenocarcinoma in dogs.
