Study Finds Need for Standardization of Immune Checkpoint Inhibitor Assays in NSCLC

The development of immune checkpoint inhibitors, including programmed death-1 and programmed death-ligand 1 (PD-L1) inhibitors, has changed the treatment methods for non—small cell lung cancer (NSCLC). There may be potential interchangeability of the clinical use of certain PD-L1 inhibitors on tumor cell membranes for NSCLC, but not for assessment of PD-L1 expression on immune cells, according to a study.

In a study, published by the Journal of Clinical Oncology, reviewed previously published studies from January 2016 to January 2017 on clinical trial and laboratory-developed PD-L1 immunohistochemistry (IHC) assays (LDAs). The researchers analyzed the effects of diagnostic methods on PD-L1 expression levels in the studies in order to address the practical issues related to tissue samples.

Use of pembrolizumab to treat NSCLC requires PD-L1 IHC testing, but nivolumab and atezolizumab are approved without testing. However, the FDA has approved complimentary PD-L1 tests for both.

“Although PD-L1 IHC testing has value as a biomarker, it has limitations. Research is ongoing to identify novel biomarkers that could be used alone or in combination with PD-L1 expression levels to improve patient selection for immunotherapy,” the researchers concluded.

Following the review, the researchers found that high concordance and interobserver reproducibility were present with the PD-L1 IHC 28-8 pharmDx, PD-L1 IHC 22C3 pharmDx, and Ventana PD-L1 SP263 clinical trial assays for PD-L1 expression on tumor cell membranes. For lower PD-L1 expression was detected with Ventana PD-L1 SP142. Additionally, immune-cell PD-L1 expression was variable and interobserver concordance was poor. Researchers also noted the variable effects on PD-L1 expression for inter- and intraturmoral heterogeneity.

The researchers suggested that the development of LDAs requires standardization before they are used for recommendations in routine clinical use. In addition, the authors noted a need for training or specialized pathologists.

“Interpretation of PD-L1 IHC assays differs from most other IHC assays in the need for appreciation and understanding of the often-heterogeneous morphology of pulmonary tumors,” the authors noted. “Therefore, specialized training is important to maintain consistency and quality of interpretation between pathologists.”