An eight-gene prognostic signature and its immune associations in gastric cancer: integrated transcriptomic and clinical analyses

Background Gastric cancer (GC) remains a major cause of cancer-related mortality worldwide. Helicobacter pylori ( H. pylori ) is a major etiological factor in gastric carcinogenesis and has been associated with alterations in the tumor immune microenvironment. However, how H. pylori -related transcriptional features intersect with the broader molecular and immune heterogeneity of established gastric cancer remains incompletely characterized. Methods Single-cell RNA-sequencing data (GSE234129) were used for exploratory comparison according to H. pylori status and to define an initial candidate gene set. An eight-gene prognostic signature was subsequently developed in TCGA-STAD and evaluated in independent gastric cancer cohorts. Model-development optimism was assessed using 1, 000 full-pipeline bootstrap resamples. Immune features were evaluated using CIBERSORT, ESTIMATE, TIDE, and immunophenoscore, while observed anti-PD-1 response was explored in the disease-matched PRJEB25780 cohort. RGS1 was further assessed in an independent immunohistochemical cohort. Results Exploratory single-cell analyses suggested differences in immune-cell composition, T-cell states, and antigen-presentation-related pathways according to H. pylori status. The eight-gene prognostic signature stratified overall survival in the TCGA-STAD cohort and two independent GEO cohorts. After full-pipeline bootstrap correction, model discrimination was modest (corrected C-index = 0.575). In TCGA-STAD, addition of the eight-gene score to a clinicopathological model improved prognostic discrimination. High-risk tumors were characterized by distinct stromal, genomic, and immune features, including higher stromal activity, lower tumor mutational burden, and differences in computational immune-response-related profiles. At the tissue level, RGS1 expression was associated with survival and selected immune-cell features. In the IHC cohort, high RGS1 expression remained independently associated with poorer overall survival (OS) after multivariable adjustment (HR = 2.36, 95% CI 1.36-4.10, p = 0.002) and was accompanied by lower CD8-positive and higher CD163-positive and FOXP3-positive cell densities. In the independent H. pylori -annotated GSE62254 cohort, the five non-ribosomal components showed nominal gene-set-level enrichment in H. pylori -positive tumors (CAMERA P = 0.044). Conclusions This study developed an eight-gene survival-associated prognostic signature and characterized its immune associations in gastric cancer. H. pylori -related findings were exploratory and did not establish H. pylori specificity of the final model. Further prospective validation is required given the modest optimism-corrected performance.