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IHC Markers Explained

PD-L1 Testing on a Biopsy — What the Score on Your Report Means

Your biopsy report has come back with a PD-L1 score and abbreviations that are not explained anywhere on the sheet. This page explains what the test measured, how the score is reported, and what to ask your oncologist next.

Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026

  • A protein, not a gene — PD-L1 is a protein on the surface of some tumour cells, detected by staining the biopsy slide.
  • Reported as a percentage — The score shows what proportion of your tumour cells — or nearby immune cells — carry the protein.
  • Usually on existing tissue — In most cases the laboratory uses your stored biopsy block. A fresh sample is not always needed.
  • One input, not a decision — The score is weighed alongside your cancer type, stage, and other test results. It does not decide treatment on its own.
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PD-L1 is a protein on the surface of some tumour cells. The test stains your biopsy tissue to count how many cells carry it. The result — a percentage score — is one of several factors your oncologist considers when assessing whether immunotherapy approaches may be relevant for your cancer type and stage.

What does a PD-L1 test measure?

PD-L1 stands for Programmed Death-Ligand 1. It is a protein on the surface of some cancer cells. The laboratory stains a thin slice of your biopsy tissue with a dye that binds to this protein, then counts what proportion of cells carry it.

The result is expressed as a percentage score. Higher means more of your tumour cells carry the protein. A score of zero means none were detectable in that sample.

The score alone is not a treatment decision. Your oncologist reads it alongside your cancer type, stage, and other biomarker results before any assessment of your options.

Terms you will see on a PD-L1 report

PD-L1
Programmed Death-Ligand 1. A protein on the surface of some tumour cells that can signal nearby immune cells to stand down rather than attack the tumour.
TPS — Tumour Proportion Score
The percentage of tumour cells that stain positive for PD-L1. Used for some cancer types, including certain lung cancers. Ranges from 0 to 100.
CPS — Combined Positive Score
A score that counts PD-L1 staining on both tumour cells and nearby immune cells. Used for some other cancer types. Calculated differently from TPS and cannot be compared to it directly.
IHC — Immunohistochemistry
The laboratory method that detects PD-L1. A dye is applied to the biopsy slide; cells carrying the protein change colour so they can be counted under a microscope.
Clone
The specific antibody kit used for the test — your report may name one such as 22C3 or SP142. Each clone is validated for specific cancer types and results from different clones cannot be compared directly.

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What to ask your oncologist about your PD-L1 result

  • Which score was reported — TPS or CPS — and what the number was
  • Which antibody clone the laboratory used
  • Whether other biomarkers such as MSI status or TMB were tested at the same time
  • What this score means for your specific cancer type and stage
  • Whether the result should be reassessed if your disease progresses

Questions families commonly ask about PD-L1 testing

Which cancers use PD-L1 testing?

PD-L1 testing is part of standard workup for several cancer types where checkpoint immunotherapy is considered — including certain non-small cell lung cancers, urothelial cancers, cervical cancers, some head and neck cancers, and some gastric cancers. For some cancer types, PD-L1 is the primary marker assessed. For others it is looked at alongside MSI status or TMB. Whether PD-L1 testing applies to your diagnosis, and which scoring method applies, is determined by your cancer type — your oncologist will confirm.

Does a high PD-L1 score mean immunotherapy will work?

Not necessarily. A higher score means more of your tumour cells carry the protein — that is one signal your oncologist considers. It does not guarantee a response. Tumours with high expression do not always respond, and in some cancer types, responses have been reported at low or undetectable expression. The score is interpreted alongside your cancer type, stage, fitness, and other biomarker results. It is one piece of a fuller picture, not a prediction on its own.

Do I need a fresh biopsy to get a PD-L1 test done?

In most cases, no. PD-L1 testing is performed on your stored biopsy tissue — the block preserved from your original procedure. Laboratories keep this for years and can run additional tests on it without a new procedure. A repeat biopsy may be needed if the original sample was too small, if the disease has changed significantly since diagnosis, or if your oncologist needs current tissue. Your team will confirm whether the existing block is sufficient.

Can a PD-L1 result change if my cancer changes?

Yes. PD-L1 expression can shift as a tumour evolves, after treatment, or at recurrence. A result from a biopsy taken some time ago may not describe the tumour as it is now. If a new biopsy is taken at recurrence or disease progression, your oncologist may request repeat PD-L1 testing on that sample. Ask your team whether a previous result should be reassessed before treatment decisions are made based on it.

Did you know?

Different antibody clones used to detect PD-L1 were each validated in separate clinical trials. A result from one clone is not reliably comparable with a result from another.

This is why your report names the specific clone used — and why the right clone for your cancer type matters before the score can be interpreted.

Source: Blueprint PD-L1 IHC Assay Comparison Project — ESMO Open

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Common questions

Frequently asked questions

Does a PD-L1 score alone decide whether I receive immunotherapy?

No. PD-L1 expression is one factor among several. Your oncologist weighs it alongside your cancer type, stage, performance status, and other biomarkers such as MSI or TMB where relevant. In some cancer types, certain approaches are considered even at low or undetectable PD-L1 expression. Ask your oncologist what your score means specifically in the context of your full diagnosis — the number on the report does not speak for itself.

What does a negative or zero PD-L1 result mean?

A negative result means no meaningful PD-L1 expression was detected in that sample. It does not mean you have no treatment options. For some cancer types, other biomarkers are more predictive than PD-L1, and decisions are guided by those. For others, a negative result does influence the approach. What it means for your individual plan depends on your cancer type and stage — your oncologist will explain this in context.

Can PD-L1 be tested on the biopsy sample I have already given?

Yes, in most cases. The test is performed on your stored biopsy tissue and most cancer workup samples are preserved for additional testing. If your report does not already include a PD-L1 result, ask your oncologist whether there is enough tissue remaining in your stored block to run the test without a new procedure.

Why does the report name a specific clone such as 22C3 or SP142?

Each clone is a different antibody kit validated in clinical trials for specific cancer types. Naming the clone confirms which test was used — because scores from one clone are not always comparable with scores from another, and some clones are validated only for specific scoring methods such as TPS or CPS. If you seek a second opinion elsewhere, share which clone was used so the team can interpret the result correctly.

My PD-L1 result is positive. Does that mean immunotherapy will work?

A positive result means PD-L1 expression was detected — one signal your oncologist takes into account. It does not mean a particular treatment will work. Response depends on many factors beyond the score, including your cancer type and overall condition. Your oncologist will explain what the result means for your specific diagnosis. The score starts a conversation; it is not a conclusion on its own.

Will my oncologist look at PD-L1 alongside other biomarkers?

Yes. For many cancer types, PD-L1 is assessed alongside MSI (microsatellite instability) and TMB (tumour mutational burden), which provide related but different information about how the immune system interacts with your tumour. Which markers are relevant depends on your cancer type. Your oncologist will explain which were tested and how the results together inform your treatment assessment.

Full index

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What Is a Biopsy?

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Types of Biopsy Compared

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Preparing for a Biopsy

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Recovery and Aftercare

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Biopsy by Body Part

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Understanding Your Report

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IHC and Molecular Markers

IHC and Molecular Markers on a Biopsy: What They Mean →

Grading and Scoring Systems

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How Accurate Is a Biopsy?

How Accurate Is a Biopsy? Errors and Second Opinions →

If Your Result Is Benign

Your Biopsy Is Benign: What It Means and What Comes Next →

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