Comparison of immunohistochemical tests in the CLOVER study by Russian society of clinical oncology

Introduction. The goal of the CLOVER study performed by the Russian Society of Clinical Oncology, was a pairwise comparison of three validated PD-L1 immunohistochemical (IHC) tests (Ventana SP142, Ventana SP263, Dako 22C3) in the patient population with non-small cell lung cancer (NSCLC). This study is the first large Russian comparative study to evaluate PD-L1 expression levels using immunohistochemistry methods. Materials and methods. The study was conducted on 473 NSCLC samples from Biobank. The IHC tests were carried out with 3 antibody clones. Four trained pathologists independently evaluated the percentage of positively stained tumor cells (TC) and immune cells (IC). To assess the correlation of TC and IC between different runs and the prognostic values of one test for another, a concordant analysis was used. Results. The number of PD-L1-positive cells (≥1 %) was higher among IC compared with TC in all three IHC tests. Pearson correlation coefficients (PCC) for TCs were 0...