PD-L1 testing: Ordering & Interpreting

Programmed death-ligand 1 (PD-L1) is an immune-related biomarker that may be expressed on the surface of several tissue types, including tumor cells. PD-L1 can predict response to immunotherapy, specifically PD-1/PD-L1 immune checkpoint inhibitors. These therapies do not directly kill the cancer cell, but rather inhibit a pathway that is protecting tumor cells from immune system attack.

The purpose of this resource is to help clinicians identify patients who may benefit from PD-L1 testing and select and interpret tests for patients with different cancer types. For more background about PD-L1 and other immunotherapy biomarkers, see the overview Evaluating Immune Checkpoint Inhibition Biomarkers.

Identifying patients for PD-L1 testing

For certain types of cancer, testing for PD-L1 expression on tumor cells may help to select patients most likely to benefit from treatment with PD-L1 inhibitors. Currently, there are six anti-PD-L1/PD-1 drugs available for clinical use in the United States, with variation in approved indications:

  • Pembrolizumab, Nivolumab, Atezolizumab and Cemiplimab require PD-L1 testing using a FDA-approved test for some indications, but for others they can be prescribed independently of PD-L1 status.
  • Durvalumab and Avelumab can currently be prescribed independently of PD-L1 status.

Table 1: Indications for anti-PD-1/PD-L1 immunotherapy

PD-L1 testing required

The following cancers may require PD-L1 testing for “on-label” use of pembrolizumab, nivolumab, atezolizumab or cemiplimab:

  • Breast, triple negative

  • Cervical

  • Esophageal*

  • Gastric/gastroesophageal junction (GEJ)

  • Head and neck squamous cell (HNSCC)*

  • Non-small cell lung (NSCLC)*

  • Urothelial*

 

PD-L1 testing not required

Anti-PD-L1/PD-1 drugs may be considered for the following cancers irrespective of PD-L1 testing, depending on other clinical criteria:**

  • Basal cell 

  • Cutaneous squamous cell

  • Endometrial

  • Hepatocellular

  • Hodgkin’s lymphoma

  • Melanoma

  • Merkel cell

  • Plural mesothelioma

  • Primary mediastinal B cell lymphoma

  • Renal cell

  • Small cell lung

  • Any microsatellite instability high (MSI-H), mismatch repair deficient (dMMR), or tumor mutational burden high (TMB-H) cancer

 

*some indications of esophageal, HNSCC, NSCLC and urothelial cancer can be treated independent of PD-L1 testing

**indications in the table are simplified for educational use; see FDA guidance for specific clinical criteria

Choosing the most useful PD-L1 assay for your patient

For patients who may benefit from PD-L1 testing, selecting the best test to assess the biomarker is not always straightforward. Different immunohistochemistry (IHC) assays are validated for different tumor types with the use of different PD-L1 antibodies, positivity cutoffs, and scoring systems. The specific test required for assessing PD-L1 expression depends on the cancer type and the specific immune checkpoint inhibitor therapy being considered.

What PD-L1 tests are available?

The FDA requires the use of specific tests to assess PD-L1 status prior to prescribing immune checkpoint inhibitor therapy for certain indications. There are currently three such tests approved by the FDA as companion diagnostics.

At least one of these tests can also be used as a complementary diagnostic for other indications, which provides information about the relative benefit of the drug but does not restrict access based on PD-L1 status.

Table 2: PD-L1 companion & complementary diagnostic tests

PD-L1 Assay

Therapy

Companion diagnostic required

Complementary diagnostic available

PD-L1 SP142

Atezolizumab

  • Triple-negative breast cancer (TNBC)

  • Urothelial carcinoma

None specified

PD-L1 28-8

Nivolumab

  • Non-small cell lung cancer (NSCLC)

  • Head and neck squamous cell carcinoma (HNSCC)

  • Non-squamous cell NSCLC

  • Urothelial carcinoma

PD-L1 IHC 22C3

Pembrolizumab

  • Cervical cancer

  • Esophageal squamous cell carcinoma

  • Gastric/gastroesophageal junction (GEJ) adenocarcinoma

  • HNSCC

  • NSCLC

  • Urothelial carcinoma

None specified
PD-L1 IHC 22C3 Cemiplimab
  •  NSCLC
 None specified

To assess PD-L1 status for cancers that do not have a required companion diagnostic or a recommended complementary diagnostic, clinicians should use the assay that matches the immune checkpoint inhibitor therapy being considered, if possible.  

Interpreting PD-L1 Test Results

The methods for assessing PD-L1 expression vary slightly between assays, as does positive cut-off values, which may range between 1-100% depending on the test and cancer type.

Table 3: PD-L1 test interpretation based on scoring method and clinical indication

Drug

PD-L1 assay

Scoring

Indications*

Positive cut-off

Atezolizumab

PD-L1 SP142

% of tumor area occupied by PD-L1 expressing tumor-infiltrating immune cells (% IC)

NSCLC

≥ 10% or ≥ 50%

TNBC

≥ 1%

Urothelial

≥ 5%

Nivolumab

PD-L1 28-8

% of viable tumor cells showing partial or complete staining

NSCLC**

HNSCC

Urothelial

≥ 1%

Non-squamous NSCLC

≥ 1%, ≥ 5%, or ≥ 10%

Pembrolizumab

PD-L1 22C3

Tumor Proportion Score (TPS) = % of viable tumor cells showing partial or complete staining

NSCLC

≥ 1%

Combined Positive Score (CPS) = # of PD-L1 staining cells (includes tumor cells, lymphocytes, macrophages) / total # of viable tumor cells X 100

Cervical 

Gastric/GEJ

HNSCC

≥ 1

Esophageal

Urothelial

TNBC

≥ 10
Cemiplimab  PD-L1 22C3 TPS NSCLC  ≥ 50%

*Indications in the table are simplified for educational use; see FDA guidance for specific clinical criteria.

** NSCLC is the only indication in which the companion diagnostic for nivolumab is required. Other indications are complementary.

Limitations

Most validation data available for PD-L1 tests relate to the use of these tests in lung cancer. There is little information about whether the available PD-L1 IHC tests are interchangeable, and standardization among available tests is currently lacking with regard to antibodies used, threshold expression levels for each antibody, and scoring algorithms used. Evidence continues to emerge from ongoing clinical trials on correlations with patient outcome.

References

Agilent. PD-L1 IHC 22C3 pharmDx Overview. Accessed 8/6/2020.

Astrazeneca UK LTD. Imfinzi® (durvalumab) highlights of prescribing information. Updated 6/2020. Accessed 8/6/2020.

Bristol Myers Squibb. Opdivo® (nivolumab) highlights of prescribing information. Updated 1/2021. Retrieved 3/31/2021.

Dako North America, Inc. PD-L1 IHC 22C3 pharmDx approval statement S021. Published 2/2021. Accessed 3/31/2021.

Dako North America, Inc. PD-L1 IHC 28-8 pharmDx approval statement S013. Published 4/2020. Accessed 8/6/2020.

EMD Serono Inc. Bavencio®(avelumab) highlights of prescribing information. Updated 6/2020. Accessed 8/6/2020.

Genentech, Inc. TECENTRIQ (atezolizumab) highlights of prescribing information. Updated 10/2020. Accessed 10/15/2020.

Merck and Co., Inc. KEYTRUDA (pembrolizumab) highlights of prescribing information. Updated 3/2021. Accessed 3/31/2021.

Regeneron Pharmaceuticals. Libtayo® (cemiplimab) highlights of prescribing information. Updated 2/2021. Accessed 3/31/2021.

Roche. Ventana PD-L1 (SP142) Assay. Accessed 8/6/2020.

Udall M et al. PD-L1 diagnostic tests: a systemic literature review of scoring algorithms and test-validation metrics. Diagnostic Pathology 2018;13:12.

Ventana Medical Systems, Inc. VENTANA PD-L1 (SP142) assay interpretation guide S009. Published 3/2019. Accessed 8/6/2020.

About

This resource was developed as part of the Maine Cancer Genomics Initiative (MCGI) and is supported by The Harold Alfond Foundation and The Jackson Laboratory. 

Updated April 2021