Comparative study of programmed cell death ligand-1 immunohistochemistry assays using 22C3 and 28-8 antibodies for non-small cell lung cancer: Analysis of 420 surgical specimens from Japanese patients.

OBJECTIVES

Multiple programmed cell death ligand-1 (PD-L1) immunohistochemistry assays are currently used as companion or complementary diagnostic tools for anti-programmed cell death-1 immunotherapies. We aimed to characterize two PD-L1 immunohistochemistry assays (Dako 22C3 and 28-8) for non-small cell lung cancer (NSCLC) in clinical laboratories.

MATERIALS AND METHODS

Surgical specimens from 420 patients with pathological stages IA to IIIA NSCLC were investigated. The archived samples were freshly cut into 5-μm-thick sections stained with antibodies 22C3 and 28-8, and tumoral PD-L1 expression was evaluated in two clinical laboratories, respectively. Overall, positive, and negative percent agreement (OPA, PPA, and NPA, respectively) at specified PD-L1 cutoffs were calculated to assess the concordance between 22C3 and 28-8 assays.

RESULTS

Tumoral PD-L1 expression of ≥ 1% was detected by either 22C3 or 28-8 assays in 176 cases (41.9%), whereas 22C3 revealed a significantly higher tumoral PD-L1 expression compared to 28-8 (median 30% vs. 10%, p < 0.0001). OPA was 89.0, 90.2, and 91.9% at 1, 25, and 50% cutoff levels. When 22C3 was compared to a standard assay 28-8, the PPA was 85.5, 98.3, and 94.9%, whereas NPA was 91.0, 89.0, and 91.6% at 1, 25, and 50%. On the other hand, when 28-8 was compared to 22C3, PPA was 84.4% at 1%, but it decreased to 58.3 and 53.6% at 25 and 50%; whereas NPA remained high (91.7, 99.7, and 99.4% at 1, 25 and 50%, respectively).

CONCLUSION

Our analysis revealed that, despite the high OPA, there was discordance in the PPA between 22C3 as a standard assay and 28-8 as a comparator assay at 25% and 50% PD-L1 cutoff levels, indicating that the results of 28-8 could be translated to those of 22C3 but not vice versa.