Could the PD-1 Pathway Be a Potential Target for Treating Small Intestinal Adenocarcinoma?

Objectives: The programmed death 1 (PD-1) pathway is upregulated in the immune microenvironment of many cancers. In this study, we examined the PD-1 pathway and the immune microenvironment of small intestinal adenocarcinomas by immunohistochemistry.

Methods: From our department pathology archives we identified 42 small intestinal adenocarcinomas from between 2000 and 2015, with blocks available for IHC studies. Tumors were immunohistochemically stained for CD3, CD4, CD8, CD20, PD-1, and programmed death ligand 1 (PD-L1) expression.

Results: PD-1 was expressed by intratumoral and peritumoral lymphocytes in 35 of 42 (83%) cases. PD-L1 expression on tumor cells and immune cells was observed in seven of 42 (17%), and 18 of 42 (43%) cases, respectively. PD-L1 was mainly expressed by histiocytes capping cancerous glands/nests at the invasive front or by most tumor cells in medullary carcinomas. All the PD-L1+ tumors also expressed PD-1. The tumors expressing PD-L1 contained more CD3+, CD4+, and CD8+ T cells, but showed a lower CD4+/CD8+ ratio than those without expression of PD-L1.

Conclusions: PD-1 and PD-L1 are highly expressed by most small intestinal adenocarcinomas. Blockage of the PD-1 pathway should be evaluated in the treatment of small intestinal adenocarcinomas.