CAP Publishes Guideline for PD-L1 Testing of Patients with Lung Cancer

Northfield, Ill. (April 17, 2024) — The College of American Pathologists (CAP) in collaboration with the International Association for the Study of Lung Cancer (IASLC), Pulmonary Pathology Society (PPS), Association for Molecular Pathology (AMP) and the LUNGevity Foundation have developed evidence-based recommendations for the testing of immunotherapy biomarkers, including Programmed Cell Death Ligand-1 (PD-L1) and tumor mutation burden (TMB) in patients with non-small cell lung carcinoma (NSCLC).

“Many lung cancer patients may benefit from therapies that can harness the immune system, including anti-PD-1 or PD-L1 therapies. However, the benefit of these therapies is not universal, and clinically validated biomarkers that can help predict response include PD-L1 expression and proposed tumor mutational burden (TMB),” explains Larissa Furtado, MD, FCAP. “This guideline is intended to provide an overview of the clinical rationale for the use of PD-L1 and tumor mutational burden (TMB) testing for patients with non-small lung cancer. It highlights the technical challenges of PD-L1 testing and interpretation, including some of the complexities introduced by the development of divergent companion diagnostic PD-L1 tests for different immune checkpoint blockade therapies. It outlines the rationale for use of TMB and the current limitations of this test for lung cancer patients.”

This guideline, now available in an early online release in the Archives of Pathology & Laboratory Medicine, was driven by production of PD-L1 assays and scoring criteria that have evolved with individual therapies. At the same time, for reasons of cost and access, PD-L1 IHC antibodies and assays developed outside of the scope of randomized controlled trials have garnered widespread use.

“Clinical trials have demonstrated that drugs that block Programmed Cell Death 1 (PD-1), and PD-L1 lead to significant improvements in both response and survival relative to conventional cytotoxic chemotherapy for patients with advanced stage NSCLC,” explained guideline update co-chair Lynette Sholl, MD, FCAP.

The expert panel recognized that the regulatory-approved diagnostics are clinically validated, and as such their use is recommended. However, most laboratories may be relying on laboratory developed tests (LDTs) because of limited access to a full suite of approved clones and platforms, as well as the increased cost of running companion diagnostic-labeled assays. “To ensure patient access to PD-L1 testing, particularly at the local level, we endorse the use of LDTs and validated PD-L1 IHC (LDTs) following technical validation against one or more of the approved companion diagnostic PD-L1 assays,” said Dr. Furtado.

With six recommendations, the guideline provides data and details regarding the efficacy and utility of PD-L1 testing of patients with lung cancer. This new guideline was developed by IASLC, PPS, the LUNGevity Foundation and the CAP Center, which develops evidence-based guidelines and consensus statements related to the practice of pathology and laboratory medicine. Through this work, the CAP and its members continually improve the quality of diagnostic medicine and patient outcomes.