# Serum Lactate Dehydrogenase as a Biomarker of Disease Burden and Chemotherapy Response in Canine High-Grade Multicentric Lymphoma

## TL;DR

High levels of lactate dehydrogenase (LDH) in blood can indicate cancer severity and treatment success in dogs with aggressive lymphoma.

## Contribution

This study demonstrates LDH as a dynamic biomarker for monitoring disease burden and chemotherapy response in canine high-grade lymphoma.

## Key findings

- Dogs with high-grade lymphoma had significantly higher LDH levels than healthy dogs.
- LDH levels decreased after chemotherapy, especially in dogs achieving complete remission.
- Thrombocytopenic dogs showed higher baseline LDH and greater reductions post-treatment.

## Abstract

Lymphoma is a common type of cancer in dogs. Blood tests that track the disease during treatment are helpful for veterinarians. One such test measures an enzyme called lactate dehydrogenase (LDH), which can be higher in cancer cases, but its significance in dogs with lymphoma is not fully explored. This study found that dogs with aggressive lymphoma had much higher LDH levels compared to healthy dogs. After chemotherapy, LDH levels dropped, especially in dogs that responded well to treatment. Dogs that went into complete remission (CR) often had their LDH levels return to normal. Additionally, dogs with lower platelet counts had higher LDH levels at diagnosis and larger decreases during treatment. Overall, LDH is a simple, inexpensive blood test that can help monitor disease burden and treatment response in dogs with high-grade lymphoma.

Serum lactate dehydrogenase (LDH) is a recognized prognostic biomarker in human lymphomas, yet its clinical significance in canine lymphoma remains insufficiently characterized. This study aimed to quantify serum LDH levels in healthy dogs and dogs with high-grade multicentric lymphoma (ML) (predominantly B-cell) and to investigate correlations between LDH levels and established clinical and laboratory prognostic indicators. Twenty-seven dogs were prospectively enrolled: healthy controls (G1, n = 7) and dogs with high-grade ML (G2, n = 20). Immunophenotyping was performed by immunohistochemistry (CD3/CD79a). LDH concentrations were measured at diagnosis (T0) and after six weeks of CHOP-based induction chemotherapy (T1). Statistical analyses included Kruskal–Wallis, Wilcoxon signed-rank, Pearson’s correlation, and mixed-effects models. Dogs with high-grade ML exhibited significantly elevated LDH levels compared to controls (median 545.5 U/L, range: 288.2–2816 U/L vs. 143 U/L, range: 66–272; p < 0.001). Dogs with thrombocytopenia had higher baseline LDH (median 746 U/L, range: 612–921; p = 0.006) and greater reductions following chemotherapy (median −1011.7 U/L, range: −159 to −2064; p = 0.004). LDH levels declined significantly after treatment (overall median reduction 50.7%; post-chemotherapy range: 60.4–752 U/L; n = 15; p = 0.013), with normalization achieved in 77.8% of dogs with complete response versus 16.7% with partial or progressive disease (p = 0.02). We confirmed that serum LDH is significantly elevated in dogs with high-grade ML and declines following effective chemotherapy, supporting its utility as a dynamic biomarker of tumor burden and treatment response. Thrombocytopenic dogs may represent a biologically distinct subset warranting further investigation.