Distribution of PD-L1 expression level across major tumor types.

Abstract

e15176 Background: Programmed death-ligand (PD-L1) expression is an efficacy predictive biomarker in cancer immunotherapy. PD-1/PD-L1 axis can restore the host immunity against malignancies causing durable tumor remissions, and thus the level of PD-L1 protein expression is of critical clinical significance. However, the knowledge of PD-L1 expression level of patients with different malignancies is still inadequate understanding. Methods: Based on the percentage of positive tumor cells (TC value) identified by immunohistochemistry (IHC) method, the protein expression of PD-L1 was divided into three groups as g1 (TC < 1%), g2 (1% ≤ TC < 50%) and g3 (TC ≥ 50%). The expressions of PD-L1 from 1772 patients with malignancies across eight types including 133 patients with liver cancer, 35 patients with bile duct cancer, 94 patients with gastric cancer, 146 patients with colorectal cancer, 48 patients with pancreatic cancer, 76 patients with melanoma cancer, 33 patients with glioma and 1207 patients with lung cancer cases were made. The relationships between cancer types and PD-L1 expression were calculated via χ2 test using SPSS v22.0. Results: The ratios of PD-L1 expression in three groups (g1, g2 and g3, respectively) across eight cancer types were 67.7, 30.8 and 1.5% in liver cancer, 65.7, 28.6 and 5.7% in bile duct cancer, 77.7, 20.2 and 2.1% in gastric cancer, 81.5, 18.5 and 0% in colorectal cancer, 64.6, 31.2 and 4.2% in pancreatic cancer, 50.5, 35.7 and 13.8% in melanoma, 30.3, 63.1 and 6.6% in glioma and 55.9, 34.0, 10.1% in lung cancer, respectively. Significant correlation between the PD-L1 expression and cancer types were found (χ2 = 140.543, Cramer’s V coefficient = 0.199, p = 5.53×10−23). The expression of PD-L1 in patients with lung cancer tended to be distributed in g3, in patients with melanoma tended to be distributed in g2, and in patients with gastric cancer, glioma, and colorectal cancer tended to be distributed in g1. Conclusions: Our study suggested the protein expression of PD-L1 was significantly heterogeneous among various cancer types and offered new references for cancer-specific characters of PD-L1 expression. As a retrospective study with a relatively small population, the conclusions of this study needed to be verified with a larger sample.