Comparison of laboratory-developed test & validated assay of programmed death ligand-1 immunohistochemistry in non-small-cell lung carcinoma

BACKGROUND & OBJECTIVES: Inhibitors of immune checkpoint regulators, programmed death-1 (PD-1) and programmed death ligand-1 (PD-L1), improve outcome in advanced non-small-cell lung carcinoma (NSCLC). Tumours expressing PD-L1 protein are more likely to benefit from this targeted therapy. Multiple concurrent clinical trials evaluating different anti-PD-1/PD-L1 therapies have validated five different immunohistochemistry (IHC) assays using varied antibody clones and staining conditions. This study was aimed at identification of a single harmonized PD-L1 assay for tumour tissue conservation and cost-effectiveness in patients with NSCLC. METHODS: The performance of low-cost, manual, laboratory-developed technique (LDT) PD-L1 IHC assay using the easily available SP142 clone was compared with trial validated Ventana SP263 IHC performed on automated Ventana staining platform on tumour sections of NSCLCs. RESULTS: Eighty cases of NSCLC were included. SP263 and SP142 stained both tumour cells and immune cells. The concordance rate of tumour cell staining was about 76 per cent, with SP263 detecting more tumour cells in 16 per cent of cases. The concordance rate of immune cell staining was only 61 per cent, with SP142 detecting more immune cells in 24 per cent of cases. The sensitivity, specificity, positive and negative predictive values of manual SP142 LDT assay against gold standard SP263 Ventana assay were 70, 94, 86 and 86 per cent, respectively, at positivity thresholds of ≥1 per cent tumour cell staining. INTERPRETATION & CONCLUSIONS: The study findings suggested that LDT using SP142 clone showed only moderate concordance with SP263 Ventana assay, and the two assays were not interchangeable. More such validation studies need to be done to generate information that can complement patient therapy in cases of NSCLC.