What does a PD-L1 positive result mean?

A PD-L1 positive result means the test found PD-L1 staining on a defined proportion of tumour cells, immune cells, or both, depending on the scoring system. It may suggest a higher chance of benefit from certain checkpoint inhibitors, but it does not guarantee that immunotherapy will work. The exact meaning depends on whether the report uses TPS, CPS, or another score and on the cancer type.

Is a higher PD-L1 score always better for immunotherapy?

Not always. In some cancers, such as certain non-small cell lung cancer settings, a higher score like TPS 50% or more can make immunotherapy more likely to be used first line. But some patients with low or even negative PD-L1 still benefit, especially when immunotherapy is combined with chemotherapy or used in settings where PD-L1 is not the only selection factor.

How is PD-L1 testing done?

PD-L1 testing is usually done by immunohistochemistry on tissue from a biopsy or surgery specimen. A pathologist examines the stained slide and reports a score such as TPS or CPS. Turnaround time varies by laboratory, and small or poor-quality samples can sometimes lead to an inconclusive result.

Can PD-L1 results differ between labs or samples?

Yes. Different assays such as 22C3, 28-8, SP263, and SP142 are not fully identical, and scoring can vary somewhat between observers and laboratories. PD-L1 can also differ between the primary tumour and metastases or change after treatment, so the timing and source of the sample matter.

If my PD-L1 is low or negative, does that mean I cannot get immunotherapy?

No. A low or negative PD-L1 result does not automatically rule out immunotherapy. Some approved regimens are used regardless of PD-L1 level, and other biomarkers or clinical factors may be more important in your case. Your oncologist can explain whether the result changes treatment choices for your specific cancer.

PD-L1 expression — Glossary | India Cancer Guide

What it is

PD-L1 expression is the amount of programmed death-ligand 1 seen on tumour or immune cells, often reported as a percentage on pathology testing. The most important practical number is the cutoff percentage used by a specific cancer type and drug label, such as tumour proportion score (TPS) 50% or higher in some non-small cell lung cancer settings. PD-L1 is a protein that can bind the PD-1 receptor on T cells and reduce anti-tumour immune activity. Because of this, PD-L1 testing is used as a predictive biomarker in several cancers to help estimate whether an immune checkpoint inhibitor may be appropriate.

PD-L1 expression is not a cancer diagnosis by itself. It is a laboratory result interpreted together with the cancer type, stage, prior treatment, molecular findings, and the exact assay used. A "high" PD-L1 result can support use of immunotherapy in some settings, but some patients with low or negative PD-L1 still respond, and some with high PD-L1 do not.

How it works

The PD-1/PD-L1 pathway is one of the body's normal immune "brakes." PD-1 is a receptor on activated T cells. PD-L1 can be expressed on tumour cells, immune cells, and some normal tissues. When PD-L1 binds PD-1, T-cell activity is dampened, which can reduce inflammation but can also let cancer cells avoid immune attack.

Checkpoint inhibitor drugs such as pembrolizumab, nivolumab, atezolizumab, durvalumab, and others are designed to block this pathway. If the pathway is blocked, T cells may recover some ability to recognise and attack cancer cells. That is why PD-L1 expression is tested: it is an indirect marker of whether the tumour may be using this immune-evasion mechanism.

PD-L1 is usually measured by immunohistochemistry (IHC) on a tumour tissue sample. Different assays use different antibodies and scoring systems, which is one reason results are not perfectly interchangeable.

Common way PD-L1 is reported	What it means
TPS (Tumour Proportion Score)	Percentage of viable tumour cells showing PD-L1 staining
CPS (Combined Positive Score)	PD-L1 positive tumour cells plus certain immune cells, divided by viable tumour cells, then multiplied by 100
Immune-cell score	Percentage or area of PD-L1 staining in tumour-associated immune cells

Evidence and uses

PD-L1 expression has become an important biomarker in modern oncology, especially for selecting or prioritising immune checkpoint inhibitors. Its role is best established in cancers such as non-small cell lung cancer, urothelial cancer, head and neck squamous cell carcinoma, gastric or gastroesophageal cancers, cervical cancer, and some triple-negative breast cancer settings. The exact meaning of the result depends on the disease and the approved treatment.

In non-small cell lung cancer, PD-L1 testing is widely used because some first-line immunotherapy decisions depend on TPS thresholds. A TPS of 50% or more has been especially important in certain treatment pathways. In other cancers, CPS or immune-cell scoring may be used instead. This is why a pathology report should always be read with the assay name and scoring method, not just the word "positive."

Important points for interpretation:

PD-L1 is predictive, not perfect. Higher expression often increases the chance of benefit from some checkpoint inhibitors, but it does not guarantee response.
Low or negative PD-L1 does not always rule out benefit. Some immunotherapy regimens are used regardless of PD-L1 level, especially in combination with chemotherapy or in specific disease settings.
Assays differ. Common commercial assays include 22C3, 28-8, SP263, and SP142. These are related but not fully identical in staining characteristics and companion-diagnostic use.
Tumour heterogeneity matters. PD-L1 can vary within different parts of the same tumour and between the primary tumour and metastases.
Timing matters. Expression may change over time or after treatments such as chemotherapy, radiation, or targeted therapy.

For patients in India, PD-L1 testing is available in many tertiary cancer centres and private pathology laboratories, but access, turnaround time, and assay standardisation can vary. In practice, Indian oncologists often interpret PD-L1 together with other biomarkers such as EGFR, ALK, ROS1, MSI, TMB, ER/PR/HER2, or HPV-related context depending on the cancer type.

Diagnosis / how it's measured

PD-L1 expression is measured on a biopsy or surgical specimen, most often by IHC performed in a pathology lab. The report usually includes the antibody clone or assay platform, the scoring method, and the final score.

Typical steps include:

A tumour sample is collected.
The pathology lab stains the tissue with a PD-L1 antibody.
A pathologist examines membrane staining in tumour cells and, in some scoring systems, immune cells.
The result is reported as TPS, CPS, or another validated score.

Pre-analytical and technical factors can affect the result. These include sample quality, fixation time, small biopsy size, decalcified bone specimens, and inter-observer variation. Because of this, a PD-L1 result should ideally come from a lab experienced in thoracic or oncologic pathology and should be interpreted using the assay validated for that treatment setting.

A simplified comparison is helpful:

Issue	Why it matters
Assay used	Different assays may classify the same sample differently
Tissue adequacy	Small or damaged samples can reduce reliability
Cancer type	The same score can mean different things in different cancers
Treatment context	First-line, later-line, and combination therapy may use different cutoffs

When to see a clinician

Ask your oncologist or pathologist to explain PD-L1 if you have a new cancer diagnosis, especially lung cancer or another cancer where immunotherapy is being considered. You should also ask if the result was reported as TPS, CPS, or another score, and which assay was used.

A clinician review is particularly important if the report says "insufficient tissue," if the score is near a treatment cutoff, or if your cancer has other actionable biomarkers. In many cases, PD-L1 is only one part of treatment planning, and a low score does not automatically mean immunotherapy is off the table.

Limitations and open questions

PD-L1 expression is useful, but it has clear limitations. Evidence shows it is an imperfect biomarker because responses occur in both PD-L1 positive and PD-L1 negative groups. Results can vary by assay, pathologist interpretation, tumour site, and timing of biopsy.

Another limitation is biological complexity. PD-L1 reflects only one part of the tumour-immune interaction. Other factors such as tumour mutational burden, microsatellite instability, interferon signaling, T-cell infiltration, and the broader tumour microenvironment also influence response.

Evidence is still evolving on how best to combine PD-L1 with other biomarkers and whether blood-based or digital pathology approaches can improve prediction. For patients and families, the key point is that PD-L1 is a helpful decision tool, not a stand-alone answer. Treatment choices should be made with an oncologist who can interpret the result in the context of the exact cancer type and current guideline-based care.

PD-L1 expression