PDCD1 and neoplasm: We used flow cytometry to study the PD1 expression of macrophages in 26 GC specimens (paired blood, non-tumor tissue, and intra-tumor tissue; Table 1), and found that intratumoral macrophages expressed a significantly higher level of PD1 than those expressed on non-tumor tissue macrophages, whereas peripheral macrophages expressed little PD1 (Fig. 1a–c).