Adjuvant Chemotherapy Is Associated With Prolonged Survival Time in Small-Breed Dogs Undergoing Amputation for Appendicular Osteosarcoma

: Adjuvant chemotherapy is a well-established treatment for large-breed dogs with appendicular osteosarcoma; however, it is unclear if it improves outcomes in small-breed dogs due to limited focused studies. This retrospective study aimed to investigate the oncologic outcomes of dogs weighting less than 15 kg with appendicular osteosarcoma that underwent curative resection with or without postoperative adjuvant chemotherapy. Endpoints were time to distant progression (TTDP) and overall survival (OS). Medical records from multiple institutions were reviewed, and 43 dogs were included in the analysis: 17 underwent surgery alone and 26 also received adjuvant chemotherapy. The median TTDP for all dogs was 265 days, with no significant difference between treatment groups. The median OS for all dogs was 270 days, and it was significantly different between amputated dogs (150 days) and those also receiving adjuvant chemotherapy (353 days, p = 0.002). In our cohort, osteosarcoma in small breeds behaved as aggressive as in large breeds. Adjuvant chemotherapy may prolong survival. Future randomised studies are needed to provide definitive evidence on the necessity of adjuvant chemotherapy to address metastatic spread in small-breed dogs with appendicular osteosarcoma.