Programmed death-ligand 1 expression in gastric cancer: correlation with mismatch repair deficiency and HER2-negative status.

Gastric cancer (GC) is one of the most common malignancies. Immunotherapy is a promising targeted treatment. The immune regulatory programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis has been used as a checkpoint target for immunotherapy. Currently, considerable discrepancies exist concerning the expression status of PD-L1 and its prognostic value in GC. We aimed to evaluate the expression rates of PD-L1 in GC, and further assess its relationship with mismatch repair (MMR), and human epidermal growth factor receptor 2 (HER2) status. We retrospectively collected 550 consecutive cases of GC in Fudan University Shanghai Cancer Center from 2010 to 2012. PD-L1, MMR protein, and HER2 status were detected by immunohistochemistry (IHC). Fluorescence in situ hybridization was further used in HER2 IHC 2+ cases. Cases with at least 1% membranous and/or cytoplasmic PD-L1 staining in either tumor cells (TCs) or tumor-infiltrating immune cells (TIICs) were considered as PD-L1 positive. The correlation between clinicopathological parameters, HER2, MMR, and PD-L1 expression status was determined using chi-squared tests. About 37.3% cases (205/550) showed PD-L1 expression in TCs and/or TIICs. 17.3% cases (95/550) showed PD-L1 expression in TCs, 34.5% (190/550) cases showed PD-L1 expression in TIICs. There were 45 deficient MMR (dMMR) cases (8.2%), which showed higher rates of PD-L1 expression compared with MMR-proficient carcinomas (60.0% vs. 35.2%, P = 0.001). HER2 was positive in 66 (12.0%) cases. The expression of PD-L1 occurred more frequently in HER2-negative group than HER2-positive cohorts (39.0% vs. 24.2%, P = 0.020). The survival analysis revealed that PD-L1 was not associated with prognosis. This study evaluated the association between the PD-L1 expression and a specific subgroup (dMMR and HER2-negative) in a large Asian cohort of GC. GC patients with dMMR and HER2-negative status exhibited higher PD-L1 expression rates. Our finding indicated that MMR and HER-2 status might be potential biomarkers for anti-PD-L1 therapy.