PD-L1 tests measure the amount of PD-L1 protein expressed on tumor cells and/or tumor-infiltrating immune cells in a biopsy using immunohistochemistry; results are reported as a percentage or a scoring metric such as the Tumor Proportion Score (TPS) or Combined Positive Score (CPS) depending on the assay.

PD-L1 expression is used as a predictive biomarker to estimate the likelihood that a tumor will respond to PD-1/PD-L1 checkpoint inhibitor immunotherapy—higher PD-L1 often correlates with greater chance of benefit, but it is not definitive (some PD-L1–negative tumors respond and some PD-L1–positive tumors do not), so clinicians interpret the result alongside other clinical factors.

PD-L1 is most commonly measured by immunohistochemistry on tumor tissue obtained during a diagnostic or surgical procedure — for example a core‑needle, incisional, excisional biopsy or a resection specimen. The tissue is fixed (typically formalin) and processed into paraffin blocks (FFPE) that the pathology lab stains and scores for PD‑L1 expression.

Some laboratories also offer blood‑based or circulating‑cell tests that measure soluble PD‑L1 or PD‑L1 on circulating tumor cells, but these are less common and methods vary by lab. For tissue testing, labs generally require sufficient tumor content and properly handled/ fixed samples (archival blocks are often acceptable); follow your testing provider’s sample instructions.

PD‑L1 testing measures how much of the PD‑L1 protein is present on tumor cells or immune cells in the tissue sample you provided; it is used as a biomarker to help guide treatment decisions—particularly whether certain immune checkpoint inhibitors (anti–PD‑1/PD‑L1 drugs) are more likely to work in some cancer types. A higher PD‑L1 score can sometimes correlate with a greater chance of response to these therapies, but it is not a measure of your overall cancer risk, a cancer screen, or a definitive prognosis on its own.

Results have important limits: different tests and scoring systems use different cutoffs, PD‑L1 expression can vary within a tumor and over time, and low or negative PD‑L1 does not rule out benefit from immunotherapy. Interpretations depend on the cancer type, the assay used, and your clinical context, so discuss your specific PD‑L1 result and what it means for treatment options with your oncologist or pathologist.

PD‑L1 tests measure the amount of PD‑L1 protein on tumor or immune cells and can help predict benefit from certain immune checkpoint inhibitors, but they are not perfectly accurate. Results vary by assay (different antibodies and platforms), scoring method (e.g., TPS vs. CPS), cutoffs used, laboratory technique, and tumor heterogeneity—so the same tumor can yield different scores depending on the sample or test used.

Clinically, PD‑L1 is a useful but imperfect predictive biomarker: many PD‑L1–high tumors do not respond to immunotherapy and some PD‑L1–low/negative tumors do. Therefore PD‑L1 results are interpreted alongside cancer type, approved drug-specific companion diagnostic criteria, other biomarkers, and clinical judgment by the treating team rather than as a standalone definitive test.

PD‑L1 testing is usually done once on tumor tissue at diagnosis or immediately before deciding on immunotherapy because results guide eligibility for PD‑1/PD‑L1 inhibitors; it is not routinely repeated for surveillance. Retesting is commonly considered when the disease progresses, a new biopsy or metastatic site is obtained, or after neoadjuvant/other systemic therapy, since PD‑L1 expression can change over time.

How often to retest should be individualized by your oncology team—archived tissue may suffice for initial testing, but a fresh biopsy is often recommended when treatment decisions change. Blood-based PD‑L1 assays are less validated and are not routinely used for serial monitoring.

No — PD-L1 test results highlight patterns of imbalance or resilience—not medical diagnoses; they measure a biomarker level that can inform how the tumor microenvironment may interact with immune therapies but do not by themselves establish or rule out cancer.

PD-L1 findings must be interpreted by a qualified clinician alongside symptoms, medical history, imaging, pathology and other laboratory or biomarker data to reach a diagnosis and guide treatment decisions.

PD‑L1 is a tumor biomarker, not a general health lab value you can raise with diet or supplements. Its level depends on tumor type, sampling site and timing, tumor heterogeneity, prior treatments, and the specific assay used, so a low result does not always mean you can’t benefit from immune‑checkpoint therapy.

Practical next steps are to discuss the result with your oncologist: they may recommend re‑testing (fresh biopsy or testing a different lesion), using a different PD‑L1 scoring method, or checking complementary biomarkers (e.g., TMB, MSI). In some cases prior treatments (radiation, certain systemic therapies) can change PD‑L1 expression, but treatments should never be used solely to try to raise PD‑L1—decisions about therapy sequencing or clinical trials should be made by your cancer team based on overall disease status and guidelines.