Comparison of carboplatin and doxorubicin-based chemotherapy protocols in 470 dogs after amputation for treatment of appendicular osteosarcoma

Background: Many chemotherapy protocols have been reported for treatment of canine appendicular osteosarcoma (OSA), but outcome comparisons in a single population are lacking. Objective: To evaluate the effects of protocol and dose intensity (DI) on treatment outcomes for carboplatin and doxorubicin-based chemotherapy protocols. Animals: Four hundred and seventy dogs with appendicular OSA. Methods: A retrospective cohort study was performed comprising consecutive dogs treated (1997-2012) with amputation followed by 1 of 5 chemotherapy protocols: carboplatin 300 mg/m² IV q21d for 4 or 6 cycles (CARBO6), doxorubicin 30 mg/m² IV q14d or q21d for 5 cycles, and alternating carboplatin 300 mg/m² IV and doxorubicin 30 mg/m² IV q21d for 3 cycles. Adverse events (AE) and DI were evaluated. Kaplan-Meier survival curves and Cox proportional hazards regression were used to compare disease-free interval (DFI) and survival time (ST) among protocols. Results: The overall median DFI and ST were 291 days and 284 days, respectively. A lower proportion of dogs prescribed CARBO6 experienced AEs compared to other protocols (48.4% versus 60.8-75.8%; P = .001). DI was not associated with development of metastases or death. After adjustment for baseline characteristics and prognostic factors, none of the protocols provided a significant reduction in risk of development of metastases or death. Conclusions and Clinical Importance: Although choice of protocol did not result in significant differences in DFI or ST, the CARBO6 protocol resulted in a lower proportion of dogs experiencing AEs, which could be advantageous in maintaining high quality of life during treatment. DI was not a prognostic indicator in this study.