Prognostic and Predictive Significance of B7-H3 and CD155 Expression in Gastric Cancer Patients

Background/Objectives: This study aimed to characterize the expression patterns of B7 homolog 3 (B7-H3) and cluster of differentiation 155 (CD155), two immune-related transmembrane glycoproteins, in resectable gastric adenocarcinoma and to elucidate their clinicopathological, prognostic, and molecular implications. Methods: The study included 112 patients who underwent gastrectomy for gastric adenocarcinoma between 2020 and 2025, along with 30 samples of normal gastric tissue obtained from sleeve gastrectomy specimens. Histological subtype, grade of differentiation, TNM stage, and invasion parameters were re-evaluated. Immunohistochemical expression of B7-H3 and CD155 was quantified for membranous, stromal and membranous/cytoplasmic staining patterns. Quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed on 29 tumor and 25 normal samples to confirm mRNA expression levels, with fold change ≥2 considered biologically significant upregulation and ≤0.5 considered downregulation. Machine learning models were developed to predict metastasis and mortality based on clinical and immunohistochemical features. Results: 78.5% of tumors were at an advanced stage (T3-T4), and metastasis was present in 22.3% of patients. Perineural invasion (PNI) and lymphovascular invasion (LVI) were observed in 67.9% and 88.4% of cases, respectively. Increased B7-H3 and CD155 expression were significantly associated with advanced tumor stage, metastasis, and the presence of PNI and LVI (all p < 0.05). In metastatic tumors, median membranous B7-H3, stromal B7-H3, and CD155 scores were 60, 130, and 190, respectively, compared with 20, 90, and 120 in non-metastatic tumors. A significant positive correlation was found between stromal B7-H3 and CD155 expression (r = 0.384, p < 0.001), indicating parallel upregulation. Quantitative RT-PCR confirmed significant overexpression of both genes in tumor tissues relative to normal controls. B7-H3 was upregulated in 75.9% and CD155 in 58.6% of samples, with co-upregulation in 55.2%. Fold-change levels were markedly higher in metastatic versus non-metastatic cases (B7-H3: 7.69-fold vs. 3.04-fold; CD155: 7.44-fold vs. 1.79-fold). ML analysis using the XGBoost model achieved 91.1% accuracy for metastasis prediction (F1-score 0.800). Key variables included pathological T4b stage, perineural invasion, N3b status, T4a stage, and CD155 score. The mortality model yielded 86.7% accuracy (F1-score 0.864), with metastasis, differentiation status, nodal involvement, age, lymph node ratio, and perineural invasion emerging as principal predictors. Conclusions: Combined evaluation of B7-H3 and CD155, supported by immunohistochemical staining and RT-PCR quantification of B7-H3 and CD155 mRNA expression levels, provides meaningful prognostic insights and supports their potential as dual molecular biomarkers for aggressive gastric adenocarcinoma phenotypes.