Abstract
BackgroundImmunohistochemistry (IHC) for programmed cell death ligand 1 (PD-L1) displays staining diversity. We compared IHC staining of PD-L1 in gastric cancer (GC) by using three commercially available antibody clones, and analyzed the correlation with the prognosis.MethodsIHC using PD-L1 antibodies (clones SP142, 28–8 and E1L3N) in 315 formalin-fixed paraffin-embedded samples was qualitatively compared at the 1, 5 and 10% cut-off by two pathologists on total, tumor and immune/stromal cells. We used computer – assisted scoring to quantitatively analyze and compare the “H-score” of PD-L1 expression in 66 samples on total cells. The antibody clone SP142 was selected to investigate the infiltration of PD-L1+CD8+ T cells using automated quantitative immunofluorescence analyses (n = 50) and the prognostic significance. The prognoses were assessed by log-rank test.ResultsPD-L1 clones SP142 and 28–8 displayed great concordance by qualitative (κ = 0.816, 0.810 for total cells and tumor cells at the 5% cut-off) and quantitative analyses (R2 = 0.7991, 0.8187 for positive percentage and “H-score”). PD-L1 clone SP142 showed the highest positivity in immune/stromal cells staining (18.41%) compared to 28–8 (7.62%), while clone E1L3N showed poor staining in both tumor and immune/stromal cells. Clone SP142, but not 28–8 and E1L3N, predicted a worse prognosis at the 5% cut-off (p = 0.0243). Both the clone SP142 and 28–8 had high inter-pathologist correlation for tumor staining (R2 = 0.9805 and R2 = 0.9853), but a moderate correlation for stromal/immune cell staining (R2 = 0.5653 and R2 = 0.5745). Furthermore, a higher density of PD-L1+CD8+ T cells was correlated with a shorter survival time (R2 = 0.0909, p = 0.0352).ConclusionsPD-L1 antibody clone SP142 was superior in cell staining, particularly in immune/stromal cell and prognosis. These findings are important for selection of PD-L1 antibody clones in the future diagnostic test.
Highlights
Immunohistochemistry (IHC) for programmed cell death ligand 1 (PD-L1) displays staining diversity
The distribution of patients in each categorical scoring class for the three assays was described for total cells, tumor cells and stromal/immune cells (Fig. 2a, b)
Higher positivity was detected in immune/stromal cells using clone SP142 (58/315, 18.41%) than clone 28–8 (24/315, 7.62%), whereas only one specimen was positive for clone E1L3N (Fig. 2b)
Summary
Immunohistochemistry (IHC) for programmed cell death ligand 1 (PD-L1) displays staining diversity. Positive PD-L1 (programmed death-ligand 1) expression by immunohistochemistry (IHC), which has been mainly used to determine PD-L1 status, is a prerequisite for PD-1 blockade therapy. PD-L1-positive staining ranges from 17 to 72% in gastric cancer (GC), and this dramatic difference might be due to the use of diverse antibody clones and the lack of a consensus regarding assessment criteria [7,8,9,10,11,12,13,14]. According to the recent clinical trials (NCT01848834 and NCT02335411), 40 to 55% [15] of GCs were PD-L1-positive using the 22C3 monoclonal antibody at a 1% cut-off value (including tumor cells and stromal or immune cells)
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