IHC, NGS and liquid biopsy — what each biomarker test actually does

IHC (immunohistochemistry) stains a slide made from your existing tumour tissue with an antibody that binds to one specific protein — such as PD-L1, HER2, or a mismatch-repair protein — so a pathologist can see how much of it is present. NGS (next-generation sequencing) works on the same kind of tissue sample but reads many genes at once, looking for mutations, gene fusions, and broader signals such as tumour mutational burden or microsatellite instability in a single run instead of one marker at a time. Liquid biopsy is different again: instead of tissue, it tests a blood sample for circulating tumour DNA (ctDNA) — fragments of genetic material a tumour sheds into the bloodstream — and is used mainly when a fresh tissue sample isn't practical to obtain.

These three tests are coordinated for CION patients through accredited partner pathology and molecular-diagnostics laboratories — this page explains what the terms mean in general; it does not interpret what your own report says about your own cancer.

General ranges only, indicative as of August 2026 — not every tumour sheds enough ctDNA to be reliably detected by liquid biopsy, which is why guideline bodies treat it as complementary to tissue testing rather than an automatic substitute.

1. 1

   A sample is collected

   IHC and NGS use an existing tissue block from a prior biopsy or surgery where possible; liquid biopsy uses a simple blood draw instead.

2. 2

   The right test is selected

   Your oncologist and tumour board choose IHC, NGS, liquid biopsy, or a combination, based on your cancer type and the clinical question being asked.

3. 3

   Processing at an accredited partner lab

   Staining, sequencing or ctDNA analysis is carried out at an accredited partner pathology or molecular-diagnostics laboratory — not run in-house at CION.

4. 4

   Your oncology team reviews the report with you

   The result is discussed at tumour board and explained to you in the context of your specific treatment options — never read in isolation from your full clinical picture.

• Single-marker question — IHC is usually enough on its own, and is often ordered first.
• Multiple possible actionable mutations — NGS is typically added to screen a broader panel in one run.
• Insufficient or unsafe-to-repeat tissue — liquid biopsy can stand in for, or supplement, tissue testing.
• Monitoring over time — liquid biopsy is sometimes repeated later to watch for resistance mutations, without a new invasive procedure.
• Inconclusive first result — a second test type may be ordered to clarify an unclear IHC or NGS finding.

Liquid biopsy depends on a tumour shedding enough circulating tumour DNA into the bloodstream for the lab to detect reliably — and not every tumour sheds at a level current assays can reliably pick up, particularly in early-stage or low-disease-burden situations. When ctDNA is found, it can be highly informative; when it isn't, that result does not rule out a mutation the way a clear, adequate tissue sample can. This is a recognised, openly discussed limitation in ASCO and CAP guidance on circulating tumour DNA testing, not a flaw specific to any one lab or assay.

This is also why oncologists often treat liquid biopsy as complementary to tissue-based IHC and NGS — used together, or in sequence — rather than as an automatic, one-for-one replacement.

• How Long Do Biomarker Results Take, and Why the Wait? — what actually happens during the days or weeks between sample collection and report.
• Not Enough Tissue for Testing: What Happens Next — the options when an existing sample can't support the test your oncologist wants.
• Do You Need a Repeat Biopsy Before Starting Immunotherapy? — when a fresh tissue sample is genuinely necessary, and when it isn't.
• Immunotherapy at CION Cancer Clinics — the full picture of how CION supports patients through the immunotherapy journey.

This page explains general IHC, NGS and liquid-biopsy terminology for education only and does not interpret any individual patient's report. Testing is coordinated at accredited partner labs. Bring your report to a consultation for a doctor's assessment of what it means for you.

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