A study evaluating 4 PD-L1 assay tests has found that one reveals statistically lower levels of programmed death ligand 1 (PD-L1) expression than the others, which could influence provider and patient decision-making.
PD-L1 is a protein in cancer tumors that is associated with disease growth and progression. Treatments targeting this mechanism have been effective at improving patient outcomes and prolonging survival, but require providers and patients to be aware of how much PD-L1 tumors are expressing.
Currently, there are four assays available to test for PD-L1: the 22c3, the 28-8, the E1L3N, and the SP142. To determine how effective each of these tests are, a team at the Yale School of Medicine in New Haven, CT reviewed 90 surgically resected non-small cell lung cancer cases and sent a sample of each to four facilities for staining. There, pathologists reviewed the samples using the four assays on each case and scored them using a unified scale.
Their analysis revealed that one of the assays, the SP142, consistently returned lower levels of PD-L1 expression than what was reported using the other three. This was also true when measuring for both tumor and immune cells. The remaining three tests did not demonstrate any significant difference.
“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,” concluded 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.”