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IHC markers explained

Synaptophysin and Chromogranin: — What Positive Means

A biopsy showing synaptophysin and chromogranin as positive is identifying the tumour's cell type as neuroendocrine — a category with its own grading system, built around a third marker called Ki-67.

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

  • Cell type, not location — Neuroendocrine positive describes what the cells are, not where the tumour started. The same markers appear in gut, pancreas and lung tumours.
  • Both together is stronger — Synaptophysin and chromogranin positive together give a more reliable identification than either marker alone.
  • Ki-67 grades the tumour — Ki-67 measures how fast the cells divide. The result assigns a grade — G1, G2 or G3 — that shapes the rest of your assessment.
  • A DOTATATE scan may follow — Many neuroendocrine tumours carry receptors visible on a DOTATATE PET-CT scan. Your oncologist will advise whether this is relevant to you.
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Synaptophysin and chromogranin are proteins found in neuroendocrine cells. When both are positive on a biopsy, the tumour cells share characteristics with the body's hormone-signalling tissue — a pattern called neuroendocrine differentiation. Ki-67, also on your report, grades how fast those cells are dividing. Your oncologist uses all three together to classify the tumour.

What do synaptophysin and chromogranin positive mean?

These proteins are normally found in neuroendocrine cells — specialised cells scattered through the gut, pancreas, lung and other organs that release hormonal and chemical signals. When both are detected by the pathologist's stain, the tumour shares those neuroendocrine characteristics.

The two markers are read together, not separately. A tumour strongly positive for one and weakly positive for the other is a different finding from one that is strongly positive for both. Your oncologist interprets the full panel in the context of the whole report.

What is Ki-67 and why does it grade the tumour?

Ki-67 is a protein present only in cells that are actively dividing. The pathologist reports it as a percentage of tumour cells.

In neuroendocrine tumours, WHO classification uses this percentage to assign a grade: G1 for a low proportion of dividing cells, G2 for a moderate proportion, and G3 for a high proportion. A separate category — neuroendocrine carcinoma — describes a more aggressive form with a different behaviour.

Grade and stage are not the same thing. Grade describes how the cells behave; stage describes how far the disease has spread. Both are needed to understand the full picture.

What the terms on your report mean

Synaptophysin
A protein stored in the vesicles neuroendocrine cells use to package and release chemical signals. Positive staining identifies the cell as neuroendocrine in origin.
Chromogranin A
A protein co-released with hormones by neuroendocrine cells when stimulated. Generally more specific for neuroendocrine origin than synaptophysin.
Neuroendocrine tumour (NET)
A tumour arising from neuroendocrine cells, most commonly in the gut, pancreas or lung. Classified separately from adenocarcinomas, with its own grading system based on Ki-67.
Ki-67 index
The percentage of tumour cells actively dividing at the time of biopsy. Used under WHO classification to assign a proliferation grade — G1, G2 or G3.
Neuroendocrine carcinoma (NEC)
A high-grade, fast-growing form of neuroendocrine cancer, managed differently from lower-grade NETs. Your report will specify which category applies to you.

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How the three markers differ

MarkerWhat it detectsWhat the result tells your team
SynaptophysinProtein in secretory vesicles of neuroendocrine cellsPositive: neuroendocrine cell origin confirmed or supported
Chromogranin AProtein co-released with hormones by neuroendocrine cellsPositive: neuroendocrine origin, typically more specific than synaptophysin alone
Ki-67Protein present only in actively dividing cellsPercentage used to assign grade G1, G2 or G3 by WHO criteria

Questions families ask after seeing these results

Does positive for both markers mean the cancer started in the neuroendocrine system?

Not necessarily. Neuroendocrine cells are distributed across many organs — the gut, pancreas, lung, adrenal glands and thyroid all contain them. A tumour positive for these markers has neuroendocrine characteristics regardless of which organ it arose in. Where it started is a separate question that imaging and additional tests will help to answer, and is not determined by the IHC result alone.

My Ki-67 is reported as low. Does that mean the situation is less serious?

A low Ki-67 means the tumour cells are dividing slowly, and that matters. But it is one factor among several. The stage — how widely the disease has spread — and the primary site affect the picture equally. A slow-dividing tumour that has spread to several sites is a different situation from a faster-dividing one found early and localised. Your oncologist uses grade and stage together, and it is reasonable to ask about both at your next appointment.

Why might my oncologist mention a DOTATATE PET-CT scan?

Many neuroendocrine tumours carry a surface receptor called the somatostatin receptor. A DOTATATE PET-CT scan uses a radioactive tracer that binds to this receptor to map where the tumour and any spread are located throughout the body. It tends to be most informative in lower-grade NETs, as higher-grade tumours may carry fewer of these receptors. Whether it is appropriate for you depends on your grade and tumour type — your oncologist will advise if it would add useful information to the assessment.

Did you know?

Neuroendocrine tumours can arise in almost any organ that contains neuroendocrine cells — the gut, pancreas, lung and adrenal gland among them. This is why the same IHC markers appear on biopsy reports from entirely different primary sites.

Because neuroendocrine cells are so widely distributed, the diagnosis sometimes comes as a surprise to patients who expected a different label on their report entirely.

Source: WHO Classification of Tumours: Digestive System Tumours, 5th Edition

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Common questions

Frequently asked questions

What does synaptophysin positive mean on a biopsy report?

It means the tumour cells contain synaptophysin, a protein found in neuroendocrine cells — cells scattered through the gut, pancreas, lung and other organs that release hormones and chemical signals. On its own it points toward neuroendocrine origin, but it is always read alongside chromogranin A and Ki-67 rather than as a standalone finding.

Is chromogranin A positive always cancer?

Not always. Chromogranin A can be detected in benign conditions, and the IHC result is interpreted in the context of the full biopsy — the cell architecture, other markers and the clinical picture together. Your oncologist will explain what the result means in your specific situation.

What is a neuroendocrine tumour?

A neuroendocrine tumour (NET) arises from neuroendocrine cells — specialised cells that behave partly like nerve cells and partly like hormone-producing cells. They occur most commonly in the gut, pancreas and lung. NETs have their own grading system based on Ki-67 and range from slow-growing tumours to fast-growing neuroendocrine carcinomas, which are a separate category.

What Ki-67 percentage separates the grades?

The thresholds for G1, G2 and G3 are set by WHO classification and vary by the organ the tumour arose in. Rather than quote a number that may not apply to your specific report, ask your oncologist which criteria were used and what grade was assigned. The grade label and what it means clinically is more useful than the raw percentage alone.

Will I need a DOTATATE PET-CT scan?

A DOTATATE PET-CT is used for neuroendocrine tumours that carry somatostatin receptors — a feature more common in lower-grade NETs. Whether it is indicated depends on your tumour grade and type, and sometimes on initial imaging findings. Your oncologist will advise if it is appropriate and what it would contribute to the assessment. It is not required for every neuroendocrine diagnosis.

Should I seek a second opinion on my IHC report?

A second pathology opinion is accepted and reasonable, particularly when the diagnosis is unexpected, markers are borderline, or the result will significantly affect your treatment plan. You would ask for the original slides or digital images to be reviewed by a pathologist at another centre. Your oncologist can help arrange this, and it need not delay treatment when organised promptly.

Full index

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What Is a Biopsy?

What Is a Biopsy? Everything You Need to Know →

Types of Biopsy Compared

Which Biopsy Will You Have? Techniques Compared →

Preparing for a Biopsy

What to Expect on the Day of Your Biopsy →

Recovery and Aftercare

After a Biopsy: Recovery, Aftercare and Warning Signs →

Biopsy by Body Part

Biopsy by Body Part: What to Expect at Each Site →

Understanding Your Report

How to Read a Biopsy Report: Terms Explained →

IHC and Molecular Markers

IHC and Molecular Markers on a Biopsy: What They Mean →

Grading and Scoring Systems

Cytology & Prostate Scoring Systems Explained →

How Accurate Is a Biopsy?

How Accurate Is a Biopsy? Errors and Second Opinions →

If Your Result Is Benign

Your Biopsy Is Benign: What It Means and What Comes Next →

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