CD8A and neoplasm: Tumor cells can overexpress CD39 compared with normal cells; however, elevated levels have been also reported in endothelial cells, cancer-associated fibroblasts (CAF) and several immune subpopulations, particularly, natural killer (NK) cells, tumor-associated-macrophages (TAM) and tumor-infiltrating lymphocytes (TILs) including Tregs and CD8+ T cells [23,24,25,26,27,28].