Appendicular Osteosarcoma in Small Breed Dogs and Cats

Introduction
Median survival time in large breed dogs with appendicular osteosarcoma (AOSA) treated with amputation and adjuvant chemotherapy is approximately 1 year. In cats with AOSA, mean and median survival times vary between 12 and 49 months and the need for adjuvant chemotherapy has been questioned. Similarly, the optimal treatment for small breed dogs (<15 Kg) with AOSA has not been determined. The study presented below evaluated survival in dogs weighing less than 15 Kg with AOSA.

Materials and methods
Members of the VSSO were asked to search medical records for dogs weighing less than 15 kg diagnosed with histopathology confirmed AOSA. Treatment groups were created (palliative treatment, amputation alone, and curative-intent treatment). Survival analysis was performed to create survival curves and determine the factors associated with survival.

Results
Forty-six small dogs were included in the study. 10 cases had palliative treatments (PT), 13 cases had amputation alone (AAT) and 23 cases had curative intent treatment (CIT).

Median survival times were 112 (PT), 277.5 (AAT) and 504 (CIT). Statistical significance was only reached when PT and CIT were compared (p=0.01 HR=3.3). Administration of chemotherapy was the single factor associated with increased survival when all cases were included (p=0.02 and HR=0.4).

Conclusions
Survival in small breed dogs treated with either amputation alone or with curative intern treatment compared favorably with reported large breed dog cases. This study suggests that chemotherapy should be part of the treatment of appendicular osteosarcoma in small breed dogs too.