To account for this differential behavior in tumor tropism and based on the data gathered from the A20 tumor model implanted into the peritoneal cavity, we observed that A20 PD-L1 WT tumor cells are protected to some extent from rejection by the host F1 CD8 T cells, likely due to PD-1-mediated inhibition of their cytotoxic function. This evidence concerns the gene CD8A and neoplasm.