Serum Lactate Dehydrogenase as a Potential Prognostic Biomarker in Dogs With Appendicular Osteosarcoma

: In human medicine, serum lactate dehydrogenase (LDH) is a well-established prognostic marker in osteosarcoma, reflecting tumour burden. This study evaluates serum LDH as a prognostic biomarker in dogs with histologically confirmed appendicular osteosarcoma undergoing a complete staging work-up. Fifty-two dogs with osteosarcoma were prospectively enrolled, and LDH levels were assessed at diagnosis, prior to any treatment. Elevated LDH was observed in 34 (65.4%) dogs. All dogs with distant metastasis had increased LDH levels. A significant association was observed between elevated LDH and metastasis (p = 0.039). To assess the impact of LDH on survival, a subgroup analysis included 38 dogs without metastasis that underwent multimodal treatment and had a minimum follow-up of 180 days. Median time to progression (TTP) and overall survival (OS) were significantly shorter in dogs with elevated LDH (157 and 169 days, respectively) compared to those with LDH within reference limits (252 and 387 days, respectively; p = 0.035 and p = 0.017). On univariable analysis, elevated LDH was the only variable associated with an increased tumour progression risk (HR = 2.26, 95% CI = 1.09-4.69, p = 0.029). Additionally, elevated LDH, absence of immunotherapy administration, and increased serum alkaline phosphatase activity were significantly associated with a higher mortality risk. These findings suggest that elevated LDH at diagnosis indicates a more advanced disease stage and poorer prognosis in dogs with appendicular osteosarcoma. LDH may aid in treatment planning and prognosis assessment. Further studies should confirm these results and explore its combination with other biomarkers to refine prognostic evaluation.