What is PD-L1 testing — and why does it decide your treatment?

PD-L1 testing measures how much of a protein called PD-L1 is present on the surface of your tumour cells and the immune cells around them, using tissue from a biopsy sample. Pathologists report the result as a percentage score — usually TPS or CPS — that estimates how "visible" your cancer may be to your immune system once checkpoint inhibitor immunotherapy is switched on, guided by NCCN and ASCO biomarker-testing standards.

PD-L1 is a protein some cancer cells use to switch off nearby immune cells, effectively hiding from them. Checkpoint inhibitor immunotherapy works by blocking that switch. A PD-L1 test doesn't diagnose your cancer or measure how advanced it is — it only estimates how much of this specific hiding mechanism is present in your particular tissue sample.

This page explains what the test is and how it's done, in general terms. It does not, and cannot, interpret your individual report — that conversation belongs with the oncologist who ordered the test and knows your complete clinical picture.

Your PD-L1 score is one input your oncology team weighs — alongside your cancer type, stage, other biomarkers, and overall health — when deciding whether checkpoint inhibitor immunotherapy is a reasonable option and which drug or combination fits your case. It is not a single number that decides everything on its own.

In several cancers, a specific immunotherapy drug is approved for use only above a minimum PD-L1 score, so the result can open or close the door to that particular option. In others, immunotherapy may still be considered at lower scores, sometimes combined with chemotherapy. This is exactly why the same PD-L1 report can lead to different treatment plans for two different patients.

A PD-L1 score, on its own, does not guarantee that a treatment will or will not work — response rates vary within every score band, and other biomarkers can matter just as much for your specific cancer.

TPS and CPS are scored differently and are not interchangeable — always check which one your report uses. For the numbers explained in more depth, see our companion page on understanding your PD-L1 score.

1. 1

   Using existing biopsy tissue

   Most PD-L1 testing uses tissue already collected during your original diagnostic biopsy or surgery. A fresh biopsy usually isn't needed unless that tissue is insufficient.

2. 2

   Sending it to an accredited lab

   Your slides or tissue block are sent to an accredited pathology laboratory for PD-L1 immunohistochemistry (IHC) staining. CION coordinates this at partner labs and does not run PD-L1 testing in-house.

3. 3

   Staining and scoring

   A pathologist stains the tissue with an antibody that binds PD-L1, then examines it under a microscope to calculate the TPS or CPS score.

4. 4

   Getting your report

   Turnaround is typically one to two weeks, depending on the lab and whether other tests run on the same sample. Your oncologist reviews the report with you at your next visit.

No. PD-L1 is the most commonly ordered immunotherapy biomarker, but it is one of several. MSI-High and dMMR status can independently support immunotherapy eligibility in some cancers regardless of the PD-L1 score, and tumour mutational burden is used in specific tumour-agnostic situations. Your oncologist decides which tests are relevant to your particular cancer — not every patient needs every test.

Because PD-L1, MSI/dMMR, and other markers are often tested from the same biopsy sample, your team may order a small testing panel rather than one test at a time, to avoid repeat biopsies wherever possible.

CION coordinates PD-L1 and related biomarker testing with accredited partner pathology laboratories, and our oncology team explains what the terminology on your report means and how it fits into your overall treatment plan. For the fuller picture of how immunotherapy is used and monitored at CION, see Immunotherapy at CION Cancer Clinics.

This page explains PD-L1 testing terminology in general terms and does not interpret any individual report. Biomarker testing itself is coordinated at accredited partner laboratories, not run in-house. A PD-L1 result, on its own, does not guarantee that immunotherapy will or will not work — only your treating oncologist, reviewing your complete case, can advise on eligibility and next steps.

Thousands have made sense of their biomarker reports with us

A report full of numbers can feel like it's deciding everything on its own. Take the first step today — our team walks this part of the journey with you.