Evaluation of outcome and prognostic factors for dogs living greater than one year after diagnosis of osteosarcoma: 90 cases (1997-2008)

Abstract

Objective: To evaluate clinical characteristics, outcome, and prognostic variables in a cohort of dogs surviving > 1 year after an initial diagnosis of osteosarcoma.

Design: Retrospective case series.

Animals: 90 client-owned dogs.

Procedures: Medical records for an 11-year period from 1997 through 2008 were reviewed, and patients with appendicular osteosarcoma that lived > 1 year after initial histopathologic diagnosis were studied. Variables including signalment, weight, serum alkaline phosphatase activity, tumor location, surgery, and adjuvant therapies were recorded. Median survival times were calculated by means of a Kaplan-Meier survival function. Univariate analysis was conducted to compare the survival function for categorical variables, and the Cox proportional hazard model was used to evaluate the likelihood of death > 1 year after diagnosis on the basis of the selected risk factors.

Results: 90 dogs met the inclusion criteria; clinical laboratory information was not available in all cases. Median age was 8.2 years (range, 2.7 to 13.3 years), and median weight was 38 kg (83.6 lb; range, 21 to 80 kg [46.2 to 176 lb]). Serum alkaline phosphatase activity was high in 29 of 60 (48%) dogs. The most common tumor location was the distal portion of the radius (54/90 [60%]). Eighty-nine of 90 (99%) dogs underwent surgery, and 78 (87%) received chemotherapy. Overall, 49 of 90 (54%) dogs developed metastatic disease. The median survival time beyond 1 year was 243 days (range, 1 to 1,899 days). Dogs that developed a surgical-site infection after limb-sparing surgery had a significantly improved prognosis > 1 year after osteosarcoma diagnosis, compared with dogs that did not develop infections.

Conclusions and clinical relevance: Results of the present study indicated that dogs with an initial diagnosis of osteosarcoma that lived > 1 year had a median survival time beyond the initial year of approximately 8 months. As reported previously, the development of a surgical-site infection in dogs undergoing a limb-sparing surgery significantly affected prognosis and warrants further study.

Figure 1

Kaplan-Meier curves of survival time after the first year for 29 dogs with osteosarcoma that underwent a limb-sparing procedure and survived > 1 year after the initial diagnosis. Dogs (n = 20) that developed a surgical-site infection after limb-sparing surgery (dashed line) survived significantly (log-rank test P = 0.002) longer after 1 year (median, 180 days; range, 25 to 1,899 days) than did the 9 dogs that did not develop surgical-site infection after limb-sparing surgery (solid line; median, 28 days; range, 8 to 282 days).

Figure 2

Kaplan-Meier curves of survival time after the first year for 90 dogs with osteosarcoma that survived > 1 year after the initial diagnosis. The 6 dogs that developed local recurrence (dashed line) survived significantly (log-rank test P = 0.029) longer after 1 year (median, 441 days; range, 25 to 1,899 days) than did the 84 dogs that did not develop local recurrence (solid line; median, 172 days; range 1 to 816 days).