PD-L1 immunoreactivity and its association with tumor grade in canine mammary carcinomas.

Programmed death ligand 1 (PD-L1) is a transmembrane protein involved in tumor immune evasion. Although widely studied in human oncology, its role in canine mammary carcinoma remains poorly characterized. We quantified pd-l1 gene mRNA levels by reverse-transcription quantitative real-time PCR (RT-qPCR), evaluated PD-L1 immunoreactivity by immunohistochemistry (IHC) in canine mammary carcinomas, and tested their association with tumor grade and epidemiologic factors using 96 formalin-fixed, paraffin-embedded tissue samples. The mean age of affected dogs was 9.6 y, with Miniature Poodles and mixed-breed dogs most frequently represented. We found no statistically significant associations between pd-l1 mRNA levels with histologic subtype or epidemiologic factors. However, PD-L1 immunoreactivity was significantly associated with tumor grade in the bivariate analysis (p = 0.017; Cramer V = 0.3), supporting the diagnostic value of PD-L1 IHC in canine mammary carcinomas and suggesting its utility as a marker of tumor aggressiveness.