Thymidine kinase 1 and lactate dehydrogenase activities in plasma and pleural effusion as biomarkers of feline mediastinal lymphoma: Clinical, viral and molecular correlates.

Feline mediastinal lymphoma is an aggressive cancer needing non-invasive methods for monitoring. This study aims to examine the correlation of thymidine kinase (TK1) and lactate dehydrogenase (LDH) levels in plasma and pleural effusion in cats diagnosed with mediastinal lymphoma and to explore how these markers relate to clinical, pathological, and genetic factors. We analyzed plasma and effusion samples from 30 cats with confirmed mediastinal lymphoma. TK1 was measured using an ELISA assay, and LDH activity and albumin levels were measured using an automatic chemical analyzer. We assessed FeLV infection, cytological grade, immunophenotype, and specific single nucleotide variants (SNVs) in KIT, BCL2, and ZEB1. Lymphoma cats had significantly higher TK1 levels than non-neoplastic controls. A positive correlation was observed between plasma and effusion TK1 levels. No correlation with LDH activity was observed. FeLV-positive cats showed higher plasma TK1 levels and a greater likelihood of elevated effusion. However, fluid TK1 levels were also higher in cats with T-cell lymphomas and those with the ZEB1 c. T > C variant; these differences were not statistically significant. No notable differences were found for LDH or the LDH-to-albumin ratio. The strong correlation and moderate agreement between plasma and pleural effusion TK1 levels potentially indicate that either sample type can be used to assess tumour activity. In contrast, the LDH values differed between the two compartments. Biological factors, including FeLV infection, T-cell phenotype, and ZEB1 variants, may impact tumour activity. This study highlights plasma TK1 as a valuable, non-invasive biomarker for monitoring feline mediastinal lymphoma. However, validation in larger cohorts is needed before clinical application.