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Osteosarcoma is the most common malignant primary bone cancer, but it is infrequently reported in cats. Feline appendicular osteosarcoma typically exhibits good prognosis when treated with surgery alone. A retrospective multi-institutional study was conducted to identify possible prognostic factors. Cats diagnosed with appendicular osteosarcoma were included if initial staging and follow-up information were available. Data including signalment, tumour characteristics, treatment modalities, and survival outcomes were collected and analysed. Fifty-six cats were included; the femur was the most frequently affected bone. Eight cats had distant metastasis at admission and an additional 9 developed metastatic disease during follow-up, resulting in an overall metastatic rate of 30%. Forty-nine (87.5%) cats underwent surgery, and 4 also received adjuvant chemotherapy. Among operated cats, median time to local progression (TTLP), time to distant progression and tumour-specific survival (TSS) were not reached. One- and 2-year survival rates were 66% and 55%, respectively. Seven (12.5%) cats received no treatment; 1- and 2-year survival rates were 25% and 0%, respectively. Operated cats had significantly longer TTLP (P < .001) and TSS (P = .001) compared with non-operated cats. Among operated cats, young age negatively impacted local tumour progression, while the presence of distant metastasis at diagnosis was associated with a higher risk of tumour-related death. This study reaffirms the good prognosis for cats with appendicular osteosarcoma undergoing surgery, but sheds light on some additional factors to consider. Accurate initial staging is recommended, as the metastatic rate may exceed many previous estimations. Surgery substantially extends survival time, whereas the role of chemotherapy remains uncertain., (© 2024 John Wiley & Sons Ltd.)

Coarsely fractionated radiation is commonly used as a method for pain control in dogs with appendicular osteosarcoma, however there is little published information on optimal protocols. The aim of this retrospective, descriptive study was to report safety and toxicity findings in a sample of dogs with appendicular osteosarcoma that had been treated with a radiation scheme of 10 Gy delivered over two consecutive days for a total of 20 Gy. Dogs were included in the study if they had osteosarcoma that was treated with the aforementioned protocol. Dogs were excluded if treated with the same protocol for any other bone tumor besides osteosarcoma or inadequate follow-up. Thirteen of the 14 patients received adjuvant therapy with pamidronate and a nonsteroidal anti-inflammatory. Nine dogs received adjuvant chemotherapy with carboplatin after radiation was complete. Within a median of 14 days, 92.8% of dogs subjectively had improved pain control. Median duration of response (DOR) was 80 days (range 20-365). The majority of patients developed VRTOG grade one toxicity, primarily alopecia. Five dogs (35.7%) developed pathologic fracture postradiation treatment. Timing of fracture was variable ranging from 24 to 250 days. This radiation protocol was well tolerated, with minimal toxicity, subjectively improved survival time, and had the benefit of being completed in two consecutive days., (© 2016 American College of Veterinary Radiology.)