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 0.71, 0.87, and 0.75 for 22C3 / SP142, 22C3 / SP263 and SP263 / SP142, respectively. PCC values for ICs were 0.45, 0.61, and 0.68 for the same pairs. A high coincidence of positive and negative results (>91 %) was obtained between the staining with antibodies 22C3 and SP263 of immuno- oncological agents in the 1st line. Conclusions. The highest correlation between IHC tests was obtained by pairwise comparison of 22C3 and SP263. Clone 22C3 can be considered as a substitute for SP263 in the first-line treatment of NSCLC. Clone SP142 showed weaker expression in TC and IC compared to the other two tests in patients with non-small cell lung cancer.