TMEM115 is an integral membrane protein of the Golgi complex with four transmembrane domains, primarily functioning in retrograde protein transport from the Golgi to the endoplasmic reticulum 1. The protein localizes to Golgi cisternae and interacts with the conserved oligomeric Golgi (COG) complex, regulating Golgi-to-ER retrograde transport 1. TMEM115 likely plays an indirect role in protein glycosylation, as its knockdown alters O-linked glycosylation profiles 1, consistent with its localization in a compartment enriched in UDP-sugars essential for protein and lipid glycosylation 2. Beyond its canonical Golgi function, TMEM115 has emerged as a significant oncogenic biomarker. Expression is significantly elevated in hepatocellular carcinoma and glioma tissues compared to normal tissues 34. TMEM115 knockdown inhibits cancer cell proliferation, migration, and invasion while reducing tumor growth in orthotopic models 34. The protein correlates with altered immune microenvironments in both HCC and glioma, showing associations with reduced CD8+ T cell infiltration, elevated PD-L1 expression, and increased M2 macrophages 34. These findings establish TMEM115 as a promising independent prognostic biomarker and potential immunotherapy target in cancer.