PDCD1 and neoplasm: Preclinical studies support this hypothesis [18]: CD73 blockade significantly enhances the activity of anti-programmed cell death (PD)-1 and anti-cytotoxic T-lymphocyte antigen-4 monoclonal antibodies in syngeneic mouse models of colon, prostate, and breast cancers [20], an anti-CD73 monoclonal antibody inhibits tumor growth and reverses the exhausted T-cell phenotype in an immunocompetent transgenic head and neck squamous cell carcinoma mouse model [21], and anti-CD73 antibody treatment has been shown to enhance gemcitabine efficacy in orthotopic PDAC mouse models [22].