PDCD1 and pancreatic neoplasm: A preclinical study proved that a CTLA-4 antagonist combined with gemcitabine was safe and tolerated in patients with metastatic PDAC (Aglietta et al., 2014), and PD-1 inhibitors along with chemotherapy showed antitumor effects on advanced PDAC patients, although single-agent checkpoint inhibitors showed disappointing limited activity in pancreatic cancer (Weiss et al., 2017).