PD-L1

PD-L1 is an immune-inhibitory ligand encoded by CD274. It can be expressed by tumor cells and immune cells. Binding to PD-1 on activated T cells suppresses T-cell signaling and cytokine production, helping normal tissues limit immune injury but also allowing tumors to evade immune attack. [P1-P2]

PD-L1 IHC is an imperfect predictive biomarker for anti-PD-1 or anti-PD-L1 therapy. Some PD-L1-high tumors do not respond, and some PD-L1-negative tumors do respond. Clinical use is defined by the exact cancer, assay, scoring system, threshold, drug label, stage, and treatment combination. [P3-P5]

CD274 encodes a type-I transmembrane ligand expressed on hematopoietic and non-hematopoietic cells. PD-L1 engagement of PD-1 reduces T-cell receptor signaling, proliferation, cytokine secretion, and cytotoxic function. [P1-P2]

PD-L1 expression can be adaptive, induced by interferon-gamma from an ongoing antitumor immune response, or constitutive, driven by oncogenic signaling, copy-number change, or pathway activation. Expression can therefore vary over time, between lesions, and after therapy. [P2-P3]

PD-L1 is measured in many cancers, including NSCLC, head-and-neck squamous cancer, urothelial cancer, gastric/GEJ cancer, cervical cancer, triple-negative breast cancer, esophageal cancer, ovarian cancer, and others. It is not an organ-specific marker and should not be used to infer the primary site. [P3-P5]

The clinically scored cell population differs: some labels score tumor cells, some combine tumor and immune cells, and some quantify immune-cell area. [P3-P4]

PD-L1 does not diagnose cancer. Histology and lineage markers establish the malignancy. PD-L1 is added after diagnosis to inform eligibility or expected benefit for selected immunotherapy regimens. [P2-P4]

In some cancers, a PD-L1 result is required by the drug label; in others, checkpoint inhibitors are approved regardless of PD-L1 level, or PD-L1 influences the choice between monotherapy and combination treatment rather than whether immunotherapy can be used at all. [P3-P5]

PD-L1 expression has inconsistent treatment-independent prognostic associations. It can reflect active immune recognition, aggressive oncogenic signaling, or both. Study results vary by tumor type, assay, cutoff, stage, and whether patients received immunotherapy. [P3]

PD-L1 should not be used alone to estimate recurrence or survival. Its validated role is usually predictive and treatment-specific rather than a general prognosis score. [P3-P5]

Higher PD-L1 expression can enrich for response to PD-1/PD-L1 blockade in several diseases. In metastatic NSCLC without an actionable driver, PD-L1 TPS can guide whether checkpoint-inhibitor monotherapy is an option, while chemo-immunotherapy can benefit patients across PD-L1 categories. [P3, P5-P6]

Other cancers use CPS or immune-cell scoring. A result is predictive only when generated by a validated assay and interpreted under the corresponding indication. MSI/dMMR, tumor mutational burden, viral status, clinical factors, and immune context can modify response independently of PD-L1. [P3-P4]

PD-L1 is dynamic and can change with inflammation, radiotherapy, targeted therapy, chemotherapy, or tumor evolution. Repeat testing may be considered when a new specimen is obtained and the result could alter treatment, but serial PD-L1 IHC is not a standard quantitative response-monitoring test. [P3]

Blood soluble PD-L1, exosomal PD-L1, and longitudinal spatial or transcriptomic immune signatures are research tools. Imaging and clinical assessment remain the main response-monitoring methods for checkpoint therapy. [P3]

PD-L1 is primarily assessed by IHC on formalin-fixed, paraffin-embedded tissue using validated antibody clones and platforms. Common assay families include 22C3, 28-8, SP263, and SP142. They are not automatically interchangeable for every tumor and treatment. [P3-P4]

Validated cytology cell blocks may be acceptable in some settings. Laboratories must control fixation, specimen age, tumor-cell count, controls, platform, and pathologist training. [P3]

RNA expression, multiplex imaging, spatial transcriptomics, and digital pathology can provide additional biological information but generally do not replace a required companion IHC assay. [P3-P4]

Tumor Proportion Score (TPS): percentage of viable tumor cells showing qualifying partial or complete membrane staining. Commonly used in NSCLC and some other settings.

Combined Positive Score (CPS): number of PD-L1-staining tumor cells, lymphocytes, and macrophages divided by the number of viable tumor cells, multiplied by 100; scores are conventionally capped at 100. Used in several upper-GI, head-and-neck, cervical, breast, and other indications.

Immune Cell (IC) score: proportion or area of tumor occupied by PD-L1-positive immune cells, depending on the assay and disease. [P3-P4]

The report should state clone, platform, specimen, scoring algorithm, numeric score or category, adequacy, cutoff used, and the specific drug/cancer context if applicable. A bare "positive/negative" result is unsafe. [P3-P4]

PD-L1-high means the specimen exceeds a specified threshold under one assay and scoring system. It suggests a higher probability of benefit in some contexts, not certainty. [P3, P5]

PD-L1-negative means the sample did not meet that cutoff; it does not prove checkpoint therapy cannot work. Combination regimens, other biomarkers, and tumor-specific approvals may make treatment appropriate despite low expression. [P3, P6]

Interpretation requires exclusion or consideration of actionable oncogenic drivers in cancers such as NSCLC, because immunotherapy sequencing and benefit can differ. [P3]

PD-L1 has spatial heterogeneity within a tumor and between primary and metastatic sites. Small biopsies may misclassify the overall tumor. [P3]

Expression changes over time and after treatment. Preanalytic variables, tissue exhaustion, decalcification, low viable-tumor-cell count, necrosis, and pathologist interpretation affect results. [P3]

Different clones and scoring algorithms can produce non-equivalent categories. A threshold validated for one drug and cancer should not be automatically transferred to another. [P3-P4]

PD-L1 is only one part of immune biology. Antigenicity, HLA presentation, T-cell infiltration, interferon signaling, immunosuppressive cells, and co-mutations can outweigh the IHC score. [P7-P9]

Lack of immune recognition: low neoantigen burden or insufficient antigen presentation can limit T-cell priming even when PD-L1 is expressed.

Defective interferon signaling: acquired loss-of-function changes in JAK1/JAK2 can prevent interferon-driven antitumor effects and PD-L1 adaptive signaling. [P8]

Antigen-presentation loss: B2M or HLA-pathway alterations can prevent recognition by cytotoxic T cells. [P9]

T-cell exclusion and suppressive microenvironment: stromal barriers, abnormal vasculature, myeloid suppressor cells, regulatory T cells, TGF-beta signaling, and metabolic suppression can block effective infiltration. [P7]

Alternative checkpoints and exhaustion: upregulation of LAG-3, TIM-3, TIGIT, or other inhibitory pathways may permit escape. Resistance mechanisms can coexist and are not captured by repeat PD-L1 staining alone. [P7-P9]

Anti-PD-1 antibodies: pembrolizumab, nivolumab, cemiplimab, dostarlimab, retifanlimab, and others depending on region and cancer.

Anti-PD-L1 antibodies: atezolizumab, durvalumab, avelumab, and others.

Dual-checkpoint combinations: PD-1/PD-L1 blockade combined with CTLA-4 or other checkpoint agents.

Chemo-immunotherapy and targeted combinations: checkpoint blockade with chemotherapy, antiangiogenic therapy, radiation, or targeted drugs. The need for PD-L1 testing varies by regimen. [P3-P6]

PD-L1 itself is not a drug class. It is an expression biomarker connected to a specific label and assay. [P4]

PD-L1 testing remains indication specific. The FDA companion-diagnostic list was updated in 2026 and continues to link individual assays, sample types, scoring rules, and therapies. This supports building the website from structured therapy-test relationships rather than one global cutoff. [P4]

New disease settings continue to appear. In February 2026, the U.S. FDA approved pembrolizumab-based therapy for selected platinum-resistant ovarian, fallopian-tube, or primary-peritoneal carcinoma with PD-L1 CPS at least 1 by an authorized test. [P10]

Research is moving beyond single-marker IHC. Spatial immune architecture, T-cell clonality, circulating tumor DNA, multiplex protein imaging, tumor genomics, microbiome factors, and composite models are being evaluated to improve prediction. [P3, P7-P9]

Perioperative immunotherapy complicates interpretation. Studies increasingly use checkpoint blockade before or after surgery, sometimes with benefit across PD-L1 categories. The biomarker's value can differ by stage and regimen, so the website should avoid presenting one universal predictive rule. [P3]

Regulatory statements describe U.S. FDA indications and should be checked against the current label for the user's country or region.