PDCD1 and neoplasm: PD-1 is expressed on tumor-infiltrating lymphocytes (TILs), which are upregulated in various types of solid tumors and related to tumor invasion and unfavorable prognosis.In contrast to solid tumors, the presence of a large number of PD-1+ TILs predicts a favorable overall survival (OS) in patients with DLBCL [10–12].