PD-L1 Testing

Last Literature Review: March 2022 Last Update:

Medical Experts


Programmed death-ligand 1 (PD-L1) is an immune-related biomarker that can be expressed on the surface of many tissue types, including tumor cells. For certain types and stages of cancer, testing for PD-L1 expression may help to identify patients most likely to benefit from treatment with PD-L1 inhibitors. Novel immunotherapies, known as immune checkpoint inhibitors, can interrupt signals generated by immune checkpoint proteins, such as PD-L1, and can enhance antitumor T-cell immunity.   Several PD-L1 inhibitors, including atezolizumab, durvalumab, nivolumab, and pembrolizumab, have been approved for a number of clinical indications and are being evaluated in multiple malignancies. The U.S. Food and Drug Administration (FDA) divides PD-L1 immunohistochemistry (IHC) tests into two groups: companion diagnostic tests, which provide information that is essential for the safe and effective use of a drug (test results are required for drug use), and complementary or codiagnostic tests, which may be used in treatment selection but are not considered essential for use of the corresponding therapy (test results are NOT required for drug use).  

Quick Answers for Clinicians

What is the difference between companion and complementary programmed death-ligand 1 (PD-L1) testing?

COMPANION programmed death-ligand 1 (PD-L1) testing is shown to be predictive of patient response to a specific immunotherapy for a type of tumor, on a specific platform. Testing is required for the specific immunotherapy to be used. COMPLEMENTARY PD-L1 testing may be predictive of patient response to a specific immunotherapy for a type of tumor, but this testing is not required to use immunotherapy. 

How do I determine the appropriate programmed death-ligand 1 (PD-L1) test to order?

Selection of the appropriate test depends on the patient’s malignancy and the intended use of the programmed death-ligand 1 (PD-L1) inhibitor. Refer to the ARUP Consult FDA-Approved Indications for PD-L1 Testing algorithm for tests that are available for specific cancer types.

Indications for Testing

PD-L1 testing may be considered for patients with specific types of malignancies to predict response to specific immune checkpoint inhibitors.

PD-L1 Laboratory Testing

PD-L1 testing recommendations depend on the drug being considered, the malignancy, and the stage of cancer. Please refer to the ARUP Consult FDA-Approved Indications for PD-L1 Testing algorithm for laboratory test selection guidance.

PD-L1 Testing Interpretive Scoring Systems

There are several interpretive scoring systems available for PD-L1 testing, including the tumor proportion score (TPS), the combined positive score (CPS), and tumor-infiltrating immune cell (IC) staining assessments.

In brief, the TPS is based on the proportion of tumor cells that express PD-L1 to the total number of tumor cells (staining and nonstaining). The CPS is calculated in a manner similar to that used for the TPS, but the CPS includes PD-L1 expression in tumor-associated lymphocytes and macrophages in addition to the ratio of PD-L1-expressing tumor cells. For the 22C3 assay, either TPS or CPS can be used. For the 28-8 assay, TPS can be used.

The selection of which scoring system to use, as well as the interpretive cutoffs, depends on the test, tumor, and indications. Refer to the ARUP Consult FDA-Approved Indications for PD-L1 Testing algorithm for more information.

ARUP Laboratory Tests

PD-L1 scoring and interpretation (with CPS or TPS) will be provided based on tumor type and origin as determined by an ARUP pathologist.