PD-L1 Immunohistochemistry Testing

Companion and complementary testing to predict treatment response

In patients with specific tumor types, PD-L1 immunohistochemistry (IHC) is indicated to predict response to treatment with PD-L1 inhibitors. The specific PD-L1 clone, scoring method, and eligibility requirements depend on the tumor type, stage of malignancy, previous treatment outcomes, and specific PD-L1 inhibitor under consideration.

PD-L1 Test menu

PD-L1 testing

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. We accept tissue block, formalin-fixed paraffin-embedded (FFPE) specimens, or three unstained slides with four microns thick FFPE tissue specimens for our PD-L1 assays.

Key testing



Available PD-L1 IHC clones by tumor type

Non-small cell lung cancer (NSCLC)

Tumor TypePD-L1 CloneDrugCutoff
Cervical cancer22C3Pembrolizumab (Keytruda)CPS >= 1
Esophageal squamous cell carcinoma (ESCC)22C3Pembrolizumab (Keytruda)CPS >= 10
Head and neck squamous cell carcinoma (HNSCC)22C3Pembrolizumab (Keytruda)CPS >= 1
Non-small cell lung cancer (NSCLC)22C3Pembrolizumab (Keytruda)TPS >= 1
Non-small cell lung cancer (NSCLC)22C3Cemiplimab-rwlcTPS >= 50
Non-small cell lung cancer (NSCLC)28-8Nivolumab combined with Ipilimumab (anti-CTLA-4)TC >= 1%
Non-small cell lung cancer (NSCLC)SP142Atezolizumab (Tecentriq)TC >= 50% or
IC >= 10%
Non-small cell lung cancer (NSCLC)SP263Atezolizumab (Tecentriq)TC >= 1%
Triple negative breast cancer (TNBC)22C3Pembrolizumab (Keytruda)CPS >= 10
Urothelial carcinoma (URC)SP142Atezolizumab (Tecentriq)IC >= 5%
CPS = (# PD-L1 + cells [tumor cells, lymphocytes, macrophages] / Total # of viable tumor cells) * 100
TPS = (# PD-L1 + tumor cells / Total # of all tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
22C3Pembrolizumab (Keytruda)CPS >= 1
CPS = (# PD-L1 + cells [tumor cells, lymphocytes, macrophages] / Total # of viable tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
22C3Pembrolizumab (Keytruda)CPS >= 10
CPS = (# PD-L1 + cells [tumor cells, lymphocytes, macrophages] / Total # of viable tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
22C3Pembrolizumab (Keytruda)CPS >= 1
28-8NivolumabTC >= 1%
CPS = (# PD-L1 + cells [tumor cells, lymphocytes, macrophages] / Total # of viable tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
22C3Pembrolizumab (Keytruda)TPS >= 1
22C3Cemiplimab-rwlcTPS >= 50
28-8Nivolumab combined with Ipilimumab (anti-CTLA-4)TC >= 1%
SP142Atezolizumab (Tecentriq)TC >= 50% or
IC >= 10%
SP263Atezolizumab (Tecentriq)TC >= 1%
TPS = (# PD-L1 + tumor cells / Total # of all tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
22C3Pembrolizumab (Keytruda)CPS >= 10
CPS = (# PD-L1 + cells [tumor cells, lymphocytes, macrophages] / Total # of viable tumor cells) * 100

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.

PD-L1 CloneDrugCutoff
SP142Atezolizumab (Tecentriq)IC >= 5%

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring. For the most up-to-date list, click here.



Pathology consultation testing

If additional interpretation or analysis is needed, request a pathology consultation.

Key testing

Highlights



Frequently asked questions

What is PD-L1?


PD-L1 is expressed on tumor cells and ligates to PD-1, which is expressed on immune cells. This interaction hampers the immune response against tumor cells. Drugs have been developed to block this interaction and boost the immune response.

Why does Mayo Clinic Laboratories offer multiple tests for PD-L1?

We currently offer four clones of the PD-L1 antibody for IHC staining: clone 22C3, clone 28-8, clone SP263, and clone SP142. Each clone is associated with a different drug and tumor type and can have unique staining patterns and interpretation guidelines.

Are the four clones equivalent?

Generally, clones 22C3, SP263, and 28-8 have similar staining patterns. Clone SP142 has a lower sensitivity and often stains fewer cells, both tumor and immune. However, because of the different therapies and tumor types associated with each clone, none of the clones should be used interchangeably. The oncologist should request the appropriate clone for the specific tumor type and therapy under consideration.

How are the PD-L1 stains scored and reported?


Interpretation of PD-L1 stains is performed by Mayo Clinic Laboratories pathologists who specialize in the particular tumor type. There are several scoring systems, including TPS, CPS, and IC for PD-L1 staining. The scoring system used will depend on the requirements for the specific tumor type, clone, and therapy of interest.

What is unique or challenging about the interpretation of PD-L1?

Both tumor cells and immune cells can express PD-L1. In tumor types that have many macrophages, such as NSCLC, it can be difficult to differentiate between the tumor cells and the immune cells. Also, PD-L1 expression can be very heterogeneic within a tumor, meaning that expression in a single biopsy may not be reflective of the entire tumor. There is also heterogeneity in the expression of PD-L1 between the primary tumor and metastatic tumor, between the primary tumor and recurrent tumor, and among multiple primary tumors.

What if I get an unexpected error when clicking a URL?

Relaunch the link to view the digital image. If the error continues, close all browser windows and relaunch from MayoACCESS/MayoLINK or click on the digital image link in the Results Available email. If the error persists, contact Mayo Clinic Laboratories at 855-516-8404.

What if my slide images are missing?

Refresh the webpage. If the images are still not displaying after several minutes and a webpage refresh, contact Mayo Clinic Laboratories at 855-516-8404 for assistance. NOTE: Images may not display immediately upon email receipt. It can take several minutes for the image to upload and be available for viewing.

What are the browser requirements for digital imaging?

We recommend using Chrome or Edge as a browser for digital imaging.

What are the monitor requirements for viewing digital slide images? 

As tech-only images are not intended for diagnostic use, there are no regulatory requirements for computer monitors used to view tech-only slide images. However, the quality of the digital slide image will improve with higher-performing monitors. 

Are digital slide images available for manual requisitions?

No. Clients wishing to access digital images for tech-only IHC/ISH stains must order electronically.

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