Abstract
Background:
Sarcoids and squamous cell carcinomas (SCC) are the most concerning equine oncological diseases. Both tumors are challenging to manage due to their invasive behavior and high prevalence of recurrences. Furthermore, squamous cell carcinomas have propensity to metastasize. Programed cell-death ligand 1 (PD-L1) has been one of the main therapeutic targets for immunotherapy in various human tumors. PD-L1 research is equine tumors is scarce and more efforts are necessary to understand the potential of this biomarker as therapeutical target.
Aim:
Evaluate the immunohistochemical expression of PD-L1 in equine sarcoids and squamous cell carcinoma.
Methods:
Thirteen equine tumors (seven sarcoids and 6 squamous cell carcinomas) were tested by immunohistochemistry and evaluated semi quantitatively to assess the percentage of positive cells.
Results:
None of the sarcoids presented PD-L1 expression. Regarding squamous cell carcinoma, 2 tumors presented <10% of labeled cells; 2 tumors presented 10-25% of labeled cells and 2 tumors presented 25-50% of labeled cells. There were statistically significant differences between sarcoids and squamous cell carcinoma regarding the expression of PD-L1.
Conclusion:
Our results point to the fact that PD-L1 could be a potential therapeutic target against SCC, and also encourage in-depth studies in this area, with larger sample sizes.

Key words: Equine, Immunotherapy, PD-L1, Sarcoid, SCC