The clinical and genetic characteristics of TMED3, a p24-family protein, across different cancer types remain incompletely understood. This study aimed to evaluate its expression patterns, prognostic relevance, epigenetic regulation, immune associations, genetic alterations, functional networks, and chemical-gene interactions across six cancer types.

Public, de-identified data from UALCAN, GENT2, the Human Protein Atlas (HPA), Kaplan-Meier Plotter, MEXPRESS, cBioPortal, TIMER2.0, the Comparative Toxicogenomics Database (CTD), STRING, and DAVID were analyzed. The clinical and genetic characteristics of TMED3 in bladder cancer (BLCA), head and neck squamous cell carcinoma (HNSC), kidney renal clear cell carcinoma (KIRC), kidney renal papillary cell carcinoma (KIRP), liver hepatocellular carcinoma (LIHC), and lung adenocarcinoma (LUAD) were analyzed. Database-reported nominal P-values were used because unified multiple-testing correction was not feasible.

In UALCAN analysis, TMED3 mRNA was upregulated in BLCA, KIRP, LIHC, KIRC, and LUAD and downregulated in HNSC. HPA data showed higher TMED3 protein expression in BLCA, HNSC, and LUAD. Kaplan-Meier Plotter analysis showed that higher TMED3 expression was associated with shorter overall survival in HNSC, KIRC, KIRP, LIHC, and LUAD, but not in BLCA, and was not significantly associated with recurrence-free survival in any of the six cancers. MEXPRESS analysis suggested an inverse association between promoter methylation and TMED3 expression. TIMER analysis showed negative correlations between TMED3 expression and CD8+ T-cell infiltration in BLCA, HNSC, and LUAD, but a positive correlation in LIHC. cBioPortal showed low TMED3 alteration frequencies across the six cancers, and STRING and DAVID analyses linked TMED3-associated genes mainly to endoplasmic reticulum-Golgi trafficking and vesicle-mediated transport pathways. CTD analysis identified azacitidine, doxorubicin, and MK-2206 as chemicals associated with altered TMED3 expression.

TMED3 is a cancer-type-specific prognostic candidate associated with shorter overall survival in five of the six analyzed cancers. Its transcript-protein discordance, methylation pattern, and immune correlations define testable biological hypotheses, but independent experimental and clinical validation is required before clinical application.