RBBP8 Is a Prognostic Biomarker Associated With Response to Immune Checkpoint Inhibitors in Advanced Gastric Cancer

The current biomarkers for immune checkpoint inhibitor (ICI) therapy have several limitations, and new ones are being explored. Retinoblastoma-binding protein 8 (RBBP8) is associated with tumor-infiltrating immune cells (TIIC) and immune checkpoint molecules. Therefore, RBBP8 may serve as a novel biomarker for ICI therapy. Thus, in this study, we investigated the relationship between RBBP8 expression and the tumor immune environment in 58 patients with pathologic T3-4 gastric cancer who underwent radical gastrectomy. Immunohistochemistry of primary tumor specimens was performed to evaluate RBBP8, TIIC, and programmed cell death ligand 1 expression. Kaplan-Meier survival and prognostic factor analyses were also performed using Cox proportional hazards regression models. Patients were divided into RBBP8 high (HG, n=29) and low (LG, n=29) expression groups, using the median RBBP8 expression as the cutoff. The LG had a significantly worse overall survival rate than the HG (log-rank test, P =0.029). Furthermore, the overall survival rate of patients in LG who were treated with ICI (n=7) was worse than that of those in HG (n=9; log-rank P =0.005). Multivariate analysis identified extensive lymph node metastasis and low RBBP8 expression as independent prognostic factors. The HG and LG showed no significant difference in the number of TIICs; however, there was a difference in the number ratios of CD4+/CD8+ ( P =0.012) and CD4+/CD3+ cells ( P <0.001). Therefore, RBBP8 expression in patients with advanced gastric cancer is a prognostic marker that affects the proportion of CD4+ T-cell infiltration and may also be a biomarker for predicting ICI treatment response.