Association of Blood Monocyte and Lymphocyte Count and Disease‐Free Interval in Dogs with Osteosarcoma

Background: Identification of biomarkers that predict outcomes in dogs with osteosarcoma (OSA) would be valuable to veterinarians and owners. Leukocyte numbers in peripheral blood are associated with outcomes in some types of cancer in humans. Hypothesis/Objectives: We hypothesized that increased numbers of monocytes would be associated with reduced disease‐free interval (DFI) in dogs with OSA. Animals: Medical data from 69 dogs with appendicular OSA treated with amputation and chemotherapy were selected for study. Methods: Retrospective study. Statistical associations were assessed by univariate and multivariate analysis. Information about DFI and leukogram values, tumor location, and serum alkaline phosphatase was abstracted from the medical record. Results: Higher numbers of circulating monocytes (>0.4 × 10³ cells/μL) and lymphocytes (>1.0 × 10³ cells/μL) before treatment were found to be significantly (P < .05) associated with shorter DFI in dogs with OSA. Other parameters associated with poor outcomes were increased alkaline phosphatase, primary tumor location, and age. Conclusion and Clinical Importance: These results indicated that pretreatment evaluation of monocyte and lymphocyte counts provided prognostic information for dogs with appendicular OSA. Notably, most animals in this study had monocyte counts within the normal reference range, indicating that variations within the reference range of leukocyte values might also have prognostic significance.