Impact of palliative-intent radiotherapy with or without chemotherapy on lameness in flat coat retrievers with localised periarticular histiocytic sarcoma - a retrospective cohort, single institution study.

Histiocytic sarcoma (HS) is a common tumour in flat coat retrievers (FCRs) often affecting periarticular tissues and joints. Palliative-intent radiotherapy, seeks to achieve local tumour control, pain relief and improve limb function. However, the effect of palliative-intent radiotherapy on analgesic levels of dogs with localised HS has not been studied. We hypothesised that palliative-intent radiotherapy could improve lameness in dogs affected by localised HS. This study aimed to assess the impact of palliative-intent radiotherapy on lameness of FCRs with localised HS. A retrospective cohort single institution study was performed. Medical records of FCR dogs with HS that received external beam radiotherapy between 2003 and 2022 were reviewed and included demographic, staging, severity of baseline lameness, therapeutic management and outcome data. Descriptive statistics, McNemar's chi-squared test, Fisher's exact test and Kaplan-Meier analysis were used for statistical analysis. Thirty-nine dogs were included with a median age of 7.2 years, 25 were male and 14 were female. HS was most commonly located in the forelimb (29 dogs, 74.3%), affecting the shoulder joint (19 dogs, 48.7%). Staging was performed in all 39 dogs with 22 (56.4%) dogs having localised HS, six (15.3%) dogs had localised HS with node metastasis and 11 (28.2%) dogs had localised HS with systemic metastasis. All dogs received palliative-intent hypo-fractionated radiation therapy, 32 (82%) dogs showed improvement in lameness. In conclusion, palliative intent radiation treatment has an analgesic effect reducing lameness or clinical signs associated with affected tumour-bearing joints.