High expression of programmed cell death protein 1 on peripheral blood T-cell subsets is associated with poor prognosis in metastatic gastric cancer

Immune checkpoints in solid tumors serve important roles in metastasis. The present study was designed to explore the expression of programmed cell death protein 1 (PD-1) on peripheral blood T-cell subsets and its role in the clinicopathological features and prognosis of patients with metastatic gastric cancer. The expression of PD-1 in peripheral blood T-cell subsets was detected in 100 metastatic gastric cancer patients prior to the first line chemotherapy by flow cytometric analysis. The potential associaton between the peripheral blood T-cell subsets PD-1 level and the clinicopathological features of patients with metastatic gastric cancer and the clinical outcomes was analyzed. The percent of high PD-1 expressed cluster of differentiation (CD)3(+), CD3(+)CD4(+) and CD3(+)CD8(+) T-cells was 20.4, 13.0 and 9.4%, respectively in patients with metastatic gastric cancer. The overall survival (OS) and progression-free survival (PFS) rate of the 100 patients with metastatic gastric cancer was 12.2 and 3.9 months, respectively. Kaplan-Meier curve with long-rank analysis indicated that patients with higher PD-1(+)/CD3(+), PD-1(+)/CD3(+)CD4(+) and PD-1(+)/CD3(+)CD8(+) levels had a worse prognosis (all P<0.05). Univariate and multivariate analysis revealed that high PD-1(+)/CD3(+) [hazard ratio (HR), 2.145; P=0.015], high PD-1(+)/CD3(+)CD4(+) (HR, 1.866; P=0.034) and high PD-1(+)/CD3(+)CD8(+) (HR, 1.817; P=0.033) level in peripheral blood were independent risk factors for predicting the survival time of patients with metastatic gastric cancer. High PD-1(+)/CD3(+), high PD-1(+)/CD3(+)CD4(+) and high PD-1(+)/CD3(+)CD8(+) expression conferred a lower overall survival rate in patients with metastatic gastric cancer. These results suggest that high PD-1 expression on peripheral blood T-cell subsets may potentially be novel prognostic biomarker for metastatic gastric cancer.