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IHC markers explained

PSA and NKX3.1 on Your Report: — What These Prostate Markers Mean

PSA and NKX3.1 are two proteins a pathologist tests in biopsy tissue to confirm whether a cancer started in the prostate. You may see them listed with a plus or minus sign on your IHC report. This page explains what each one is and what the result means.

Medically reviewed by Dr. Mohammed Imaduddin, Surgical Oncologist, MBBS · MS (General Surgery) · M.Ch (Surgical Oncology) · Last reviewed September 2026

  • Confirms origin — These markers help the pathologist decide whether a tumour, wherever it was found, started in the prostate.
  • Two is more reliable than one — PSA and NKX3.1 are reported together because each has different strengths, and together they give a more complete picture.
  • A positive result is not a treatment plan — These markers confirm where the cancer came from. What to do about it is a separate conversation with your oncologist.
  • Negative does not rule prostate out — A negative result on one or both markers does not automatically mean the cancer is not prostate cancer. The full panel and clinical picture decide.
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PSA and NKX3.1 are proteins tested by IHC to confirm whether a tumour originated in the prostate. A positive result on either marker supports prostate origin. Pathologists use both together because NKX3.1 remains detectable in tumours where PSA signal has faded, particularly in high-grade or metastatic disease.

What do PSA, NKX3.1 and IHC mean on a pathology report?

PSA (Prostate-Specific Antigen)
A protein produced mainly by the cells lining the prostate gland. When detected in tumour tissue by IHC, PSA supports the conclusion that the cancer originated in the prostate. It can occasionally be positive in a small number of other cancer types, so it is always read alongside other markers rather than on its own.
NKX3.1
A transcription factor — a protein that controls gene activity — produced almost exclusively by prostate epithelial cells. NKX3.1 is driven by the androgen receptor, which means it often stays detectable even when tumour cells have become too abnormal to produce PSA. Many pathologists consider it the more specific prostate marker of the two.
IHC (Immunohistochemistry)
A laboratory staining technique in which thin slices of tumour tissue are treated with antibodies. Each antibody binds only to its target protein. A positive result means that protein was detected in the tumour cells; a negative result means it was not. The technique helps trace where a cancer originated by identifying which proteins the tumour cells are making.
Positive (+)
The marker was detected in the tumour cells. A positive PSA or NKX3.1 result supports prostate origin. Intensity is sometimes scored as weak, moderate or strong; your pathologist weighs all of these details together when drawing a conclusion.
Negative (−)
The marker was not detected. A single negative result does not automatically rule out prostate origin. The pathologist considers the full panel of markers alongside your clinical history before reaching a conclusion.

Why do pathologists test for PSA and NKX3.1 together?

These two markers are ordered when the cancer's origin is not obvious from the biopsy alone. This most often happens when cancer is found at a site such as a lymph node, bone or liver, and the pathologist needs to trace it back to its source.

PSA has been used in prostate IHC panels for decades and is widely recognised. NKX3.1 was added to panels because it holds its signal more reliably in high-grade tumours where PSA expression can weaken or disappear entirely.

Neither result on its own decides the diagnosis. Your pathologist reads both markers together, alongside every other stain on the panel and your full clinical history.

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How do PSA and NKX3.1 differ from each other?

FeaturePSANKX3.1
What it isA secreted protein made by prostate gland cellsA gene-control protein made almost exclusively by prostate epithelium
Specificity for prostateHigh; occasionally positive in salivary gland tumours and rare breast cancersAmong the highest of any prostate marker; rarely positive in other tissue types
In high-grade (poorly differentiated) cancerExpression may weaken or be lostUsually maintained, making it valuable for aggressive tumours
In metastatic prostate cancerCan be positive, though signal may be weakerOften well preserved even in distant metastatic deposits
How the result is reportedPositive or negative; sometimes with an intensity scorePositive or negative

Did you know?

NKX3.1 expression is regulated by the androgen receptor — the same pathway that drives prostate cancer growth. Because of this, NKX3.1 often remains detectable in metastatic deposits long after PSA staining has faded, giving pathologists a way to confirm prostate origin even in very abnormal, high-grade cells.

This is why tumours of unknown primary are now routinely stained for NKX3.1 alongside PSA whenever prostate cancer is being considered as the source.

Source: CAP (College of American Pathologists) — IHC Testing in Tumours of Unknown Primary

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Common questions

Frequently asked questions

My IHC report says PSA positive. Does that confirm prostate cancer?

A positive PSA result on IHC strongly supports prostate origin, but it does not confirm the diagnosis on its own. Your pathologist considers PSA alongside NKX3.1, any other markers on the panel, and your clinical history before reaching a conclusion. A small number of other tumour types can also express PSA. The final interpretation — and what it means for your care — comes from your oncologist, who reads the full pathology report alongside your imaging and clinical findings.

PSA was negative on the IHC but the doctor still thinks it is prostate cancer. How is that possible?

PSA expression can fade in high-grade prostate cancers and in tumours that have been treated previously. When that happens, NKX3.1 often remains positive because it is driven by a different, more stable pathway. A panel that shows NKX3.1 positive while PSA is negative can still support a prostate origin diagnosis. Your oncologist and pathologist make this call together; a negative PSA alone does not rule the cancer out.

What does NKX3.1 positive mean on a lymph node biopsy?

It means the cells in the lymph node contain a protein produced almost exclusively by prostate tissue. This supports the conclusion that the cancer in the lymph node originated in the prostate, even though it has now spread. Your oncologist will use this result, together with imaging and other findings, to confirm the source and plan your care accordingly.

My blood PSA level is normal. How can the tumour be PSA positive on IHC?

Blood PSA and IHC PSA measure different things. The blood test measures how much PSA the prostate is releasing into the bloodstream. The IHC test detects the protein inside tumour cells in the biopsy tissue. A tumour can produce PSA that the stain detects, even when the blood level is not raised. The two results are independent of each other and answer different questions.

Why did the pathologist test so many markers, not just PSA?

No single IHC marker is perfectly specific to one cancer type. The more markers that point in the same direction, the more confident the origin conclusion. Panels typically include markers expected to be positive in the cancer being considered, alongside markers expected to be negative, ruling out other origins at the same time. PSA and NKX3.1 are the core prostate markers, but others may be added depending on what alternative diagnoses are possible.

Can PSA and NKX3.1 tell my oncologist which treatment to use?

These markers confirm where the cancer started — they do not directly determine treatment. Once prostate origin is established, your oncologist uses your stage, grade, extent of spread and overall health to decide what is most appropriate for you. If you have questions about the treatment options being considered, ask your oncologist to explain what the confirmed origin means for the path forward in your specific case.

Full index

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Preparing for a Biopsy

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Biopsy by Body Part

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Understanding Your Report

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IHC and Molecular Markers

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Grading and Scoring Systems

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How Accurate Is a Biopsy?

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If Your Result Is Benign

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