Immunohistochemical assays incorporating SP142 and 22C3 monoclonal antibodies for detection of PD-L1 expression in NSCLC patients with known status of EGFR and ALK genes

Different immunohistochemical (IHC) assays were approved for PD-L1 expression examination on tumor cells in qualification to immune-checkpoint inhibitors therapy in NSCLC patients. These assays have some similarities, but also very serious differences. We assessed 2 IHC tests for PD-L1 expression evaluation in NSCLC tumors with different pathological diagnoses and genetic abnormalities. We enrolled 48 NSCLC patients (median age: 65 years) with known status of EGFR and ALK genes. We compared the effectiveness of PD-L1 expression examination of two IHC assays with 22C3 (Dako) and SP142 antibodies (Ventana). IHC tests were performed in resected tissue samples and in cellblocks from bronchoscopy biopsies (formalin-fixed paraffin-embedded). IHC staining was carried out on Dako Autostainer Link 48 and Ventana Benchmark GX. The percentage of tumors with PD-L1 expression of ≥5% and ≥50% on tumor cells was significantly (p<0.05) higher in assay with 22C3 (66.7% and 45.8%) than with SP142 antibody (39.6% and 22.9%). The median percentage of tumor cells with PD-L1 expression was significantly (p<0.0001) higher in test with 22C3 than with SP142 antibody. Percentage of squamous cell carcinoma (SCC) patients with PD-L1 expression was significantly higher than of non-SCC patients. Large group of patients without PD-L1 expression on tumor cells was identified among patients with common EGFR mutations and ALK rearrangement. Our results support that the highest PD-L1 expression on tumor cells occurs in SCC patients and in adenocarcinoma patients without common, druggable genetic abnormalities. The above mentioned results were clearly visible in IHC assay with 22C3 (strong cell staining).