Emerging evidence suggests that the efficacy of immunotherapy in patients with advanced HER2-negative gastric cancer differs between Asian and non-Asian populations. This review examines potential factors contributing to these disparities, including differences in demographic and clinicopathologic characteristics, somatic mutations, molecular subtypes, tumor immunity, Helicobacter pylori (H. pylori) infection, dietary habits, and gut microbiome composition. These factors may serve as predictors of immunotherapy response in gastric cancer patients. For example, the prevalence of molecular subtypes and somatic mutations have been linked to variations in immunotherapy efficacy between Asian and non-Asian populations. In addition, differences in H. pylori infection rates, dietary habits, and gut microbiota composition may influence systemic immune responses, and consequently, immunotherapy outcomes. Understanding the factors contributing to these disparities in immunotherapy response is crucial for optimizing treatment strategies and improving outcomes for patients with gastric cancer. Further research into the mechanisms underlying racial and ethnic disparities in immunotherapy response is needed to identify potential biomarkers predictive of immunotherapy response in diverse patient populations.

Immunotherapy, particularly immune checkpoint inhibitors (ICIs) programmed death-ligand 1/programmed death-1 (PD-L1/PD-1) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), has heralded a new era of tumor treatment. Although ICIs have clinical benefits, their complex heterogeneity and diverse resistance mechanisms critically limit their efficacy. Neoantigens, arising from tumor-specific alterations, offer novel targets for individualized immunotherapy, because of their high immunogenicity and tumor specificity. In the past decade, neoantigen-based tumor vaccines have been demonstrated to be a promising immunotherapy strategy to prime the tumor-specific immune response. These therapeutic vaccines include peptide vaccines, nucleic acid vaccines, and dendritic cell (DC) vaccines, and are categorized according to the neoantigen source and delivery method. In vivo, neoantigens are processed and presented by antigen-presenting cells (APCs) via the peptide-Major Histocompatibility Complex (pMHC) for T cell recognition, thereby triggering specific immune responses. Because DCs, the most potent APCs, play crucial roles in antitumor immunity, neoantigen-based DC vaccines provide a promising therapeutic strategy. A series of global clinical trials are exploring the safety, feasibility, and efficacy of neoantigen-based DC vaccines in tumors. This review focuses on current progress in clinical research on neoantigen-based DC vaccines in the treatment of solid tumors.