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CION Cancer Clinics
Why SDHB faults carry the highest risk of spread | CION Cancer Clinics
Among the SDH genes, a fault in SDHB is the one most linked to paragangliomas that spread beyond where they started. It does not make a tumour more likely, and many SDHB carriers never develop one. But when a tumour does grow, it is more often in the abdomen, more often quiet on hormone tests and more often able to spread. That is why SDHB carriers are watched closely for life. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- Why is SDHB treated differently from the other SDH genes?
- What makes an SDHB tumour different from the others?
- What usually happens when an SDHB tumour is found?
- The words you will meet, in plain language
- How does SDHB compare with SDHD?
- What this page cannot tell you
- Four things families believe about SDHB, and what is true
- Common questions about SDHB
The short answer
Why is SDHB treated differently from the other SDH genes?
Because its tumours behave differently. Of the five SDH genes, a fault in SDHB is the one most strongly linked to a paraganglioma that spreads to the bones, liver, lungs or distant lymph nodes. Doctors call this a metastatic paraganglioma. The gene does not make a tumour more likely. It changes what a tumour is likely to do.
A lower chance of a tumour, but higher stakes if one grows
Compared with SDHD, a fault in SDHB is less likely to lead to any tumour at all, and many carriers live their whole lives without one. The concern is the smaller group who do develop a tumour. Their tumours are more often in the abdomen or chest, are often larger when found, and carry a higher chance of spread than tumours linked to the other SDH genes.
Why the plan is built around that
Because spread is the real risk, SDHB carriers are offered regular scans instead of waiting for symptoms or relying on hormone tests alone. Anyone who has had an SDHB tumour removed is followed up for life, because spread can appear many years later.
A raised chance of spread is a reason to watch closely. It is not a prediction about any one person.Four differences
What makes an SDHB tumour different from the others?
Doctors see these four features again and again in SDHB tumours. None of them is certain in any one person.
Where it grows
SDHB tumours more often grow outside the adrenal gland, along the nerves of the abdomen, pelvis and chest. Tumours in these places are found later than a lump in the neck, because nothing can be seen or felt.
Most common sites
- The abdomen and pelvis
- The chest, beside the heart or spine
- Less often, the adrenal gland or neck
What it releases
Many paragangliomas release adrenaline-like hormones that cause headaches, sweating and a pounding heart. SDHB tumours more often release noradrenaline or dopamine, or very little at all, so the classic warning signs can be missing.
A normal hormone test does not rule out an SDHB tumour.How it grows
Inside the tumour, the broken SDH enzyme lets a chemical called succinate build up. The cell then behaves as though it is short of oxygen, switching on growth signals and new blood vessels. This is thought to be part of why SDHB tumours are more aggressive.
Other tumours it is linked to
Less often, an SDHB fault is linked to tumours outside the nerve tissue. This is one reason a carrier's scans cover the whole abdomen.
- A rare SDH-deficient kidney cancer
- A rare stomach or bowel tumour called a GIST
- Very rarely, a pituitary tumour
Not sure whether this applies to you?
Ask an oncologistFrom first scan to follow-up
What usually happens when an SDHB tumour is found?
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A tumour is found on a scan or after symptoms
Often by chance on a scan done for something else, or after high blood pressure, headaches or abdominal pain. In a known carrier it is usually found on a planned surveillance MRI.
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Hormone tests and a whole-body scan
Blood or urine tests measure the hormones the tumour may release, including a dopamine breakdown product that SDHB tumours often make. A special PET scan, often a gallium DOTATATE scan, looks for other tumours or spread.
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Surgery, planned with care
Removing the tumour completely is the main treatment. If it releases hormones, blood pressure tablets are started some weeks before the operation so that surgery is safe.
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The tumour is stained in the laboratory
The pathologist checks whether the SDHB protein is missing from the tumour cells. A missing stain points to a fault in one of the SDH genes and confirms that a blood test for an inherited fault is needed.
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Follow-up for life
Because spread can appear years or even decades later, SDHB patients stay on a follow-up plan for life, with hormone tests and scans at intervals their team sets.
On your report
The words you will meet, in plain language
- Paraganglioma
- A tumour of the nerve tissue that runs alongside the spine, from the base of the skull to the pelvis. Most are not cancer.
- Phaeochromocytoma
- The same kind of tumour when it grows inside the adrenal gland, which sits on top of the kidney.
- Metastatic
- Spread to places this tissue is not normally found, such as bone, liver, lungs or distant lymph nodes. This is what doctors now mean by a malignant paraganglioma.
- SDHB staining
- A laboratory test on the tumour itself. A missing stain means any one of the SDH genes may be faulty, not only SDHB.
- Germline
- Present in every cell from birth, and so inheritable. The opposite is somatic, a fault found only inside the tumour.
- Penetrance
- How often a fault actually leads to a tumour across everyone who carries it. For SDHB it is lower than most families expect.
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Side by side
How does SDHB compare with SDHD?
SDHB
SDHD
Less likely to cause any tumour
More likely to cause a tumour over a lifetime
Tumours often in the abdomen, pelvis or chest
Tumours often in the head and neck
The highest chance of spread among the SDH genes
Spread is much less common
Usually one tumour at a time
Several tumours at once are common
Same effect whichever parent passed it on
Usually causes tumours only when inherited from the father
Being straight with you
What this page cannot tell you
It cannot tell you your own chance of a tumour, or the chance that a tumour you have had will spread. Published figures for SDHB vary a great deal between studies. Early studies came from families referred because several people were already ill, which made the risk look higher than it now appears. Studies so far are small, and very few include Indian families.
It cannot read your report
What your specific variant means is a question for the counsellor who ordered the test. The same gene name can carry different weight depending on the exact change and how the laboratory has classified it. A variant of uncertain significance in SDHB, meaning a change nobody can yet call harmful or harmless, is not a confirmed fault and should not be treated as one.
Who this does not apply to
If your family's fault is in SDHD, SDHC, SDHA or SDHAF2, the picture on this page is not yours. It does not apply to someone whose paraganglioma was tested and showed no inherited fault. Most people with high blood pressure or headaches do not need this test at all.
If a relative had a paraganglioma and nobody mentioned a gene test, ask the helpline whether your family should be offered one.Commonly believed
Four things families believe about SDHB, and what is true
"SDHB means I will get cancer."
Most SDHB carriers never develop a tumour. The raised chance of spread applies to the tumours that do form, and regular scans are designed to find those while they are small.
"My hormone test was normal, so there is no tumour."
SDHB tumours can release very little hormone. That is why carriers are offered MRI scans as well as blood or urine tests, and why a normal blood test alone is not enough.
"The tumour was removed, so it is over."
Spread from an SDHB tumour can appear many years after a successful operation. Lifelong follow-up is the standard, even when the surgeon removed everything visible.
"The lab said SDHB was missing, so we carry an SDHB fault."
A missing SDHB stain on the tumour means one of the SDH genes may be faulty. Only a blood test for inherited faults says which gene, and whether relatives can be tested.
Questions we are asked
Common questions about SDHB
Is an SDHB paraganglioma always cancer?
No. Most paragangliomas, including many linked to SDHB, stay where they started. Doctors now accept that every paraganglioma has some potential to spread, and SDHB tumours have more than most. A tumour is called metastatic only once it has spread to places such as bone, liver or lungs.
How often do SDHB tumours spread?
Figures vary widely between studies, and almost none come from Indian families. What is consistent is that SDHB carries the highest chance of spread among the SDH genes. Your team will talk about the risk for your own tumour using its size, its site and what the laboratory found.
Why are SDHB carriers offered MRI rather than CT?
MRI uses no radiation, which matters for scans repeated across a whole lifetime, and for children. It shows the abdomen, pelvis and chest well. CT or a PET scan is used when a finding needs a closer look, or when surgery is being planned.
Should my children be tested for SDHB?
Usually yes, in childhood, because SDHB tumours can appear in children and teenagers and early scans help. Testing is generally offered around the time surveillance would begin. A counsellor will discuss the right time for your family and explain it to the child in a way that suits their age.
Can spread from an SDHB tumour be treated?
Yes. The aim is usually long-term control rather than removing every trace. Options include surgery, radiotherapy, targeted radioactive treatments such as MIBG or DOTATATE therapy, chemotherapy and newer tablets. Small studies suggest some SDHB tumours respond well to a chemotherapy tablet called temozolomide.
Does an SDHB fault affect the kidneys?
A small number of carriers develop a rare kind of kidney cancer. It is one reason surveillance scans include the kidneys. If a kidney tumour is found in a carrier, it is usually removed early, and the laboratory checks whether it has lost the SDHB protein.
Will a result affect marriage or insurance?
India has no dedicated law on genetic discrimination, so some families worry about disclosure. A counsellor can help you think through who needs to know and when, including in marriage conversations. Raise insurance before testing, not afterwards, since some people choose to arrange cover first.
Where do we start if a relative had an SDHB tumour?
Ask for a referral to a genetic counsellor, or call the CION helpline to be pointed to the right clinic. Bring old scan reports, operation notes and the tumour pathology report if you have them. You can ask for the conversation to be held in Telugu.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
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Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- GeneReviews (NCBI) — Hereditary Paraganglioma-Pheochromocytoma Syndromes
- MedlinePlus Genetics — SDHB gene
- National Cancer Institute — Pheochromocytoma and Paraganglioma Treatment (PDQ) – Patient Version
- MedlinePlus Genetics — Hereditary paraganglioma-pheochromocytoma
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Hereditary paraganglioma and phaeochromocytoma explainedThe condition behind all five SDH genes, from the startSurveillance for SDH gene carriersWhich checks carriers have, and how oftenWhole-body MRI for SDHx carriersWhat the scan day is like, and how to prepareTesting the family for SDH genesWho should be tested next, and in what order
Talk to us
Does your family carry an SDHB fault?
Tell us who was diagnosed and whether a gene test was done. We will explain what surveillance makes sense and help you arrange counselling and scans. One helpline serves every CION centre.