Evaluation of PD-L1 expression and its prognostic implications in canine mammary tumors

Recent advances in cancer research involve special focus on the role of immune check points in cancers and have pointed out that the cancer cells sometimes find ways to use immune checkpoint proteins as a shield to evade immune action. The current study involved 37 spontaneous canine mammary gland tumors to evaluate the prognostic value of PD-L1. Histologically, out of 37 cases 30 cases were classified as malignant and 07 as benign tumours. Higher relative expression of PD-L1 mRNA by real time PCR was observed in malignant tumours as compared to benign tumors. Kruskal-Walli’s test was used for determining the prognostic value based on mean gene expression values of PD-L1 between the groups of animals and revealed a statistically significant (P≤0.05) difference between recurrence and alive groups and dead and alive groups. However, comparison between groups with death and recurrence did not show any statistical difference (P>0.05). Higher PD-L1 expression was associated with poor postsurgical outcome with either death or recurrence leading to poor overall survival. Statistical analysis of Kaplan- Meier curves of follow up period of dogs revealed statistically significant (p≤0.05) difference in survival time between dogs having PD-L1 over and under expression with an approximate period of survivability for over expressed cases was 135 days. The results from the current study indicated that PD-L1 gene expression could be used as a candidate target for the use of existing immune therapy for clinically advanced cases of canine mammary gland tumours.