LGALS9C (galectin 9C) is a galactoside-binding protein located on chromosome 17 that functions as a carbohydrate-binding molecule with immunoregulatory properties. The protein binds galactosides and is involved in negative regulation of CD4-positive, alpha-beta T cell proliferation [GO annotations] and negative regulation of type II interferon production, suggesting a role in immune suppression. LGALS9C is expressed in both cytosolic and nuclear compartments where it can modulate gene expression [GO annotations]. In cancer biology, LGALS9C has emerged as a clinically relevant immunomodulator. In EGFR-mutated lung adenocarcinomas with high PD-L1 expression, LGALS9C is upregulated in immune cell compartments alongside other inhibitory immunomodulators (CD276, HAVCR2), contributing to an immunosuppressive microenvironment characterized by increased T regulatory cell infiltration 1. Additionally, LGALS9C was identified as a tumor suppressor gene with copy number loss in a pancreatic adenocarcinoma case associated with Shwachman-Diamond syndrome 2. Epigenomic studies have revealed associations between LGALS9C DNA methylation and metabolic phenotypes; region-based methylation analysis identified LGALS9C as significantly associated with triglyceride level changes in response to fenofibrate treatment 3, suggesting potential involvement in lipid metabolism regulation.