Medical Oncologist
CION Cancer Clinics
SDHx gene faults: which tumours and how much risk | CION Cancer Clinics
An SDHx fault mainly raises the risk of paragangliomas and phaeochromocytomas, tumours of nerve-related tissue that can grow from the neck to the pelvis. A smaller risk applies to a rare stomach tumour and a rare kidney cancer. How high the risk is depends on the gene, and for some genes on which parent passed it on. This page explains each risk plainly. 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
- Which tumours does an SDHx fault raise the risk of?
- Which parts of the body are affected?
- How does your team work out your own risk?
- The words you will meet, in plain language
- How do SDHB and SDHD risks compare?
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about SDHx cancer risk
The short answer
Which tumours does an SDHx fault raise the risk of?
Mainly paragangliomas and phaeochromocytomas, which are tumours of nerve-related tissue in the neck, chest, abdomen, pelvis or adrenal gland. A smaller risk applies to a rare stomach tumour called GIST and a rare kind of kidney cancer. The risk is raised, not certain, and it differs a great deal from gene to gene.
Are these tumours cancer?
Most paragangliomas grow slowly and stay where they started. Some spread to bones, lungs, liver or lymph glands, and doctors cannot always tell from the first scan which ones will. For that reason every tumour in a carrier is taken seriously, even one that looks harmless.
Why the gene matters more than the label
An SDHB fault carries a higher chance that a tumour will spread. SDHD faults tend to cause several tumours in the head and neck, usually only when inherited from the father. SDHC and SDHA faults carry a lower risk that is still being measured. Your counsellor will explain which of these applies to your family.
A raised risk is a reason for planned checks. It is not a forecast that a tumour will appear.Where tumours appear
Which parts of the body are affected?
These tumours can grow anywhere from the base of the skull to the pelvis. Where they appear shapes the symptoms and the checks.
Head and neck
Tumours near the carotid artery, the ear or the nerves of the neck. They rarely release hormones, so blood tests often miss them and scans find them instead.
May show up as
- A painless lump in the neck
- Pulsing or ringing in one ear
- Hoarse voice or trouble swallowing
Chest, abdomen and pelvis
Tumours here, and in the adrenal gland, often release adrenaline-like hormones. They are the ones most linked with SDHB, and the ones most likely to spread.
May show up as
- Attacks of headache, sweating and a racing heart
- Blood pressure that is hard to control
Stomach
A gastrointestinal stromal tumour, or GIST, of a type that has lost the SDH machine. It tends to appear in younger people and behaves differently from the common kind of GIST.
Kidney and others
A rare kidney cancer that has lost the SDH machine, mostly with SDHB. Pituitary tumours have also been reported, but only rarely, and the evidence is limited.
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Ask an oncologistWorking it out
How does your team work out your own risk?
Which gene carries the fault
This is the biggest single factor. The report names the gene, and each gene has its own pattern of tumour sites and chance of spread.
Which parent it came from
For SDHD and SDHAF2 this matters a great deal. A fault from the father carries the usual risk. A fault from the mother carries a much lower one.
Whether you have had a tumour
Someone who has already had one tumour is more likely to have another. Their checks are usually closer and more frequent than for a relative who has stayed well.
What the family history shows
Who had tumours, where, and at what age helps show how the fault behaves in your family, though relatives can still differ.
What the first checks find
Baseline hormone tests and a scan show whether anything is already there. Your plan is then set around those results.
On your report
The words you will meet, in plain language
- Penetrance
- How often a fault actually leads to a tumour across everyone who carries it. For SDHx genes it is never all of them.
- Metastatic
- A tumour that has spread from where it started to another part of the body. This is what doctors mean by a malignant paraganglioma.
- Functional tumour
- A tumour that releases hormones into the blood. These cause most of the symptoms people notice.
- Metanephrines
- Breakdown products of adrenaline-like hormones, measured in blood or urine to check whether a tumour is active.
- SDH-deficient
- A tumour whose cells have lost the SDH machine. The pathologist can see this with a special stain.
- Multifocal
- More than one tumour, in different places, at the same time. This is common with SDHD.
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Side by side
How do SDHB and SDHD risks compare?
SDHB
SDHD
Tumours more often in the abdomen and chest
Tumours more often in the head and neck
Higher chance a tumour will spread
Lower chance of spread
Usually one tumour at a time
Several tumours are common
Risk applies whichever parent passed it on
Risk mainly when passed on by the father
Commonly believed
Four things families tell us, and what is actually true
"My blood pressure is normal, so I have no tumour."
Many head and neck tumours release no hormones and never affect blood pressure. They are found on scans, which is why a normal reading does not replace a planned scan.
"The tumour was removed, so the risk has gone."
The fault is still in every cell. A new tumour can appear elsewhere years later, and a removed one can come back, so checks continue for life.
"SDHA is the mildest, so I can ignore it."
SDHA carries a lower risk, but tumours linked with it can still spread. The evidence is thinner, so your team will agree a sensible plan rather than none at all.
"Only older people get these tumours."
Inherited tumours often appear younger than usual, sometimes in teenagers. That is why checks for some carriers begin in childhood.
Being straight with you
What this page cannot tell you
It cannot give you a personal risk figure. Published estimates vary widely because these tumours are rare, the studies are small and many of them came from families who were already unusually affected. That tends to make the numbers look higher than they are for a relative found through testing.
It cannot read your report
Two people with a fault in the same gene can carry different spelling changes that behave differently. What your specific variant means is a question for the counsellor who ordered the test, not for a search engine.
Who this does not apply to
Most people with high blood pressure, or with a relative who had an ordinary kidney or stomach cancer, do not need SDHx testing. It is meant for families where a paraganglioma, a phaeochromocytoma or a known fault has already been found. Tumour testing to choose a treatment belongs under targeted therapy.
If a relative had one of these tumours and was never offered testing, the helpline can tell you whether a referral makes sense.Questions we are asked
Common questions about SDHx cancer risk
Will I definitely get a tumour if I carry an SDHx fault?
No. Many carriers never develop a tumour, and the chance differs a lot between the five genes. Carriers who do develop one are often found early, while the tumour is small, because they were having planned checks.
Which SDHx gene carries the highest risk?
SDHD carries a high chance of a tumour when inherited from the father, mostly in the head and neck. SDHB carries the highest chance that a tumour will spread. Your counsellor will weigh both for your own family.
What symptoms should I report straight away?
Sudden attacks of severe headache with a pounding heart, sweating and paleness need same-day medical attention. A new neck lump, ringing in one ear or a hoarse voice should be reported to your team promptly, not at the next routine visit.
Can a child develop one of these tumours?
It is uncommon but it does happen, especially with SDHB. That is why children in carrier families are usually offered testing and, if positive, checks from childhood rather than waiting until adult life.
Does an SDHx fault raise the risk of breast or bowel cancer?
No clear link has been shown with the common cancers. The known risks are for paragangliomas, phaeochromocytomas, a rare stomach tumour and a rare kidney cancer. Ordinary screening for common cancers still applies as for anyone else.
Does pregnancy change the risk?
Pregnancy does not cause a tumour, but an undiscovered hormone-releasing tumour can be dangerous during pregnancy and delivery. Carriers planning a pregnancy should have hormone tests first and tell the obstetric team.
What happens if a tumour has already spread?
Options include surgery, targeted radiation treatments that seek out these tumours, radiotherapy, chemotherapy and newer tablet treatments. Many people live with the disease for a long time. An oncologist plans this with you.
Should my brothers and sisters be tested?
Yes, once your fault is confirmed. Each full brother or sister has an even chance of carrying it. A test for your known fault gives them a clear answer, and those who do not carry it can stop worrying.
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)
Medical Oncologist
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 — Hereditary paraganglioma-pheochromocytoma
- National Cancer Institute — Pheochromocytoma and Paraganglioma Treatment (PDQ) – Patient Version
- MedlinePlus Genetics — SDHD gene
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
Why SDHB carries the highest risk of spreadThe gene that is watched most closely, explainedSurveillance for SDHx carriersThe checks that find tumours earlyHereditary paraganglioma and phaeochromocytomaThe tumours themselves, in plain languageSDHx positive: what happens nextThe first steps after a positive result
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Tell us which gene is on the report and who in the family has had a tumour. We will help you reach a counsellor who can put the risk in context. One helpline serves every CION centre.