Genetic Variants and Soluble Isoforms of PD-1/PD-L1 as Novel Biomarkers for Pancreatic Ductal Adenocarcinoma (PDAC) Susceptibility and Prognosis

Background: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive neoplasm often diagnosed at advanced stages. Immune checkpoint molecules, particularly programmed cell death protein-1 (PD-1) and its ligand PD-L1, are pivotal in tumor immune evasion. Genetic polymorphisms in PD-1/PD-L1 and their soluble isoforms (sPD-1/sPD-L1) may influence individual susceptibility to cancer and disease progression. Therefore, this study was conducted to examine the correlation between PD-1/PD-L1 gene polymorphisms, serum levels of sPD-1/sPD-L1, and their association with PDAC susceptibility, severity, and prognostication. Methods: This case–control study was performed with 150 PDAC patients and 150 controls. Clinical and laboratory data, including tumor markers (CA19-9 and CEA), were recorded. Allele-specific PCR was utilized to genotype PD-1 (rs6749527 and rs7421861) and PD-L1 (rs2297136, and rs4143815). sPD-1/sPD-L1 were quantified with ELISA. Mapping of the Kaplan–Meier survival curve of mutant genes was performed. Results: The rs7421861 AG and GG and rs4143815 GG genotypes, together with their G-alleles, were linked to increased PDAC risk and greater tumor burden. In contrast, the rs2297136 GG genotype and G-allele conferred protection against PDAC development. Serum sPD-L1 levels, rather than sPD-1, were markedly elevated in PDAC patients, progressively increased with tumor grade, and correlated with tumor markers. Also, higher PD-L1 gene expression was associated with lower overall survival. Conclusions: PD-1/PD-L1 genetic variants, particularly rs7421861 and rs4143815, along with sPD-L1 levels, correlate with PDAC susceptibility and disease severity. These findings endorse the prospects of integrating immune checkpoint genetic variants and soluble biomarkers for early identification, risk stratification, prognostication, and personalized therapeutic strategies in PDAC management.