Efficacy and tolerance of short cycles of palliative radiotherapy in advanced anal sac adenocarcinomas in dogs

Abstract Successful management of advanced anal sac gland adenocarcinomas (AGASACA) often requires a multimodal approach. In recent years the role of palliative radiotherapy (pRT) has become increasingly more important, mainly in dogs with severe local clinical signs. This study describes efficacy and tolerance of short cycles of pRT. Retrospective single-institution study including dogs with AGASACA treated with at least one short cycle of pRT (IMRT, 4Gy BID for two consecutive days). All dogs were staged with CT and followed to death. Outcome measures were PFS and OST from the first pRT. Potential prognostic factors were evaluated. Twelve dogs were included (one stage II, four stage III, seven stage IV). Three dogs had one cycle, seven had two cycles, and two had three cycles of pRT. All dogs experienced a clinical benefit after pRT. One dog also had surgery, four systemic treatment, and five both. Eleven dogs died during the follow-up (four for local progression, six for systemic progression, one unknown). The median PFS was 198 days (95% CI 98—298) and the OST was 250 days (95% CI 124—376). Mild, acute, short-term GI toxicity occurred in seven dogs (five G1; two G2). None of the dogs experienced clinically relevant late toxicity. Short cycles of radiotherapy can be effectively used as a palliative treatment for advanced AGASACA with minimal toxicity. The small number of patients did not allow to assess the benefits of combining RT with other treatment modalities or the identification of meaningful prognostic factors.