Predict treatment response 

Options for companion and complementary diagnostic assays

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.

The FDA List of Cleared or Approved Companion Diagnostic Devices is frequently updated and provides current guidance for treatment indications and scoring.

Which test should I order?

22C3  | Programmed Death-Ligand 1 (PD-L1) (22C3), Semi-Quantitative Immunohistochemistry, Manual

Required specimen:

  • Tissue block, formalin-fixed paraffin-embedded; or
  • Three unstained slides, four micron thick, formalin-fixed paraffin-embedded tissue

288PD  | Programmed Death-Ligand 1 (PD-L1) (28-8), Semi-Quantitative Immunohistochemistry, Manual

Required specimen:

  • Tissue block, formalin-fixed paraffin-embedded; or
  • Three unstained slides, four micron thick, formalin-fixed paraffin-embedded tissue

SP142  | Programmed Death-Ligand 1 (PD-L1) (SP142), Semi-Quantitative Immunohistochemistry, Manual

Required specimen:

  • Tissue block, formalin-fixed paraffin-embedded; or
  • Three unstained slides, four micron thick, formalin-fixed paraffin-embedded tissue

SP263  | Programmed Death-Ligand 1 (PD-L1) (SP263), Semi-Quantitative Immunohistochemistry, Manual

Required specimen:

  • Tissue block, formalin-fixed paraffin-embedded; or
  • Three unstained slides, four micron thick, formalin-fixed paraffin-embedded tissue

If additional interpretation or analysis is needed, request PATHC/Pathology Consultation.

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 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.


Learn more about how to order these tests at your institution.