PD-L1 assays are used to test expression of the PD-L1 protein on a patient’s tumor to provide customized treatment options for drugs that may be more effective than chemotherapy in lung cancer.
The research team reviewed 90 surgically resected non-small cell lung cancer (NSCLC) cases (stages I-III) and sent a sample of each to four facilities for staining. A group of 13 pathologists at 7 institutions then reviewed the samples, using 4 different assays on each case, and scored them using a unified scoring system. A comprehensive statistical analysis was then performed on the scores collected.
Currently, there are four drugs with four PD-L1 assays (22c3, 28-8, E1L3N, and SP142) available; but only the 22c3 test is required by the FDA for prescription of a targeted anti-PD-1 drug (pembrolizumab), while the others are not yet required for prescription of other PD-1 axis drugs.
Analysis revealed that one of the assays, SP142, systematically returned statistically lower levels of PD-L1 expression than the other three. This was true in both tumor and immune cells using any test. The remaining three assays available (28-8, E1L3N, and 22c3) showed no significant difference between them, according to researchers.
“Our data shows that the SP142 assay shows significantly lower levels of PD-L1 expression. This observation may limit the use of this assay in PD-L1 testing moving forward,” said David L. Rimm, MD, PhD, first author on the study and a Professor of Pathology and of Medicine (Medical Oncology), Yale School of Medicine. “However, the other three assays seem equivalent, which is good news for the future when other PD-1 axis drugs with assay-specific diagnostics gain FDA approval.”