What should you know about PD-L1 immunohistochemistry?

PD-L1 is a protein that can be present on tumour cells or nearby immune cells. In immunohistochemistry, a pathologist applies a prepared antibody to thin sections of tissue. A visible staining pattern is then assessed under a microscope. The report may describe whether staining is present, where it is seen, and how the laboratory's scoring method applies to that cancer type.

A result is one part of the picture. Tumour type, stage, other pathology findings, previous treatment, symptoms, and general health may also influence treatment. A result does not diagnose cancer on its own and does not guarantee that a particular medicine will work.

Ask whether the test used tissue from your original [Biopsy](/treatments/diagnostics-and-staging/biopsy/) or a later sample, and whether there was enough material for testing. Clarify the staining location, scoring method, and whether the result is considered suitable for the treatment being discussed. If the sample was small, the team may explain limitations or consider another test.

Keep a copy of the pathology report and ask how PD-L1 fits with imaging, molecular tests, and your treatment choices. The laboratory method is described further under [Immunohistochemistry](/technology/immunohistochemistry/).

The test itself does not usually create an emergency. Contact your clinical team about a report you do not understand, a delayed result affecting a treatment appointment, or new symptoms from the illness or treatment. Seek urgent help for severe breathing difficulty, sudden confusion, fainting, or rapidly worsening symptoms.

What tissue was tested? Which scoring system and threshold are shown? Was staining found on tumour cells, immune cells, or both? How reliable is the sample for this result? Does it change the treatments under consideration, and are other pathology or molecular results needed?