Pembrolizumab, an anti-PD-1 immune checkpoint inhibitor, is the sole immunotherapy approved by the FDA for treating advanced PDAC in patients whose tumors are either mismatch repair deficient (dMMR) or microsatellite instability high (MSI-H) and with no other alternative options available [164,165] PDAC has been considered resistant to immunotherapy due to several challenges within the tumor microenvironment. The gene discussed is PDCD1; the disease is neoplasm.