Medical Oncologist
CION Cancer Clinics
The rare cancers where genetic testing is offered as routine | CION Cancer Clinics
A handful of rare cancers are linked so strongly to a single inherited fault that genetic testing is offered as a matter of course, without waiting for a family history. This page names them, explains why rarity itself is the clue, and sets out what happens once one of these is diagnosed in you or your child. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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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 rare cancers mean genetic testing is offered as routine?
- Which specific rare cancers are on this list?
- What happens once one of these rare cancers is diagnosed?
- Terms that come with a rare-cancer diagnosis
- A common cancer, versus one of these rare cancers
- Does a rare-cancer diagnosis always mean an inherited fault?
- What families get wrong about rare cancer diagnoses
- Common questions about rare cancers and genetic testing
A short, specific list
Which rare cancers mean genetic testing is offered as routine?
A small group of rare cancers are linked so strongly to a single inherited fault that testing is offered as a matter of course, without waiting for a family history conversation. If you or your child has been diagnosed with one of these, a genetic referral is standard practice, not something you need to request specially.
Why rarity itself is the clue
These cancers are so uncommon in the general population that finding one at all is unusual. When a cancer this rare does occur, an inherited fault explains a disproportionate share of cases, which is why testing criteria for these specific cancers are far more relaxed than for common cancers like breast or bowel cancer.
Age often matters even more here
Several of these cancers are rare at any age, but almost always point to a gene when they occur in a child. A rare adult cancer and the same rare cancer in a child are treated very differently by a genetic counsellor.
If your pathology report names one of these cancers, ask directly whether a genetic referral has already been arranged.The short list
Which specific rare cancers are on this list?
Each is linked to a different gene or syndrome, so naming the exact cancer matters to your counsellor.
Retinoblastoma
A rare childhood eye cancer. Testing is offered to almost every child diagnosed, because a large share of cases carry an inherited fault, especially when both eyes are affected.
Adrenocortical carcinoma
A rare cancer of the adrenal gland. In children especially, it is strongly associated with an inherited syndrome that also raises risk of several other cancer types.
Paraganglioma and phaeochromocytoma
Rare tumours of specialised nerve tissue. A large share of these tumours, more than most other cancer types, are linked to an inherited fault, even when there is only one tumour.
Medullary thyroid cancer
A specific, uncommon type of thyroid cancer. Its link to a single gene is strong enough that testing is recommended for essentially everyone diagnosed with it.
Not sure whether this applies to you?
Ask an oncologistWhat happens next
What happens once one of these rare cancers is diagnosed?
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The exact diagnosis is confirmed on pathology
These are specific, named cancer types, so an accurate pathology report is the starting point for everything that follows.
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A genetic referral is arranged, often automatically
For this group of cancers, many treatment centres refer to genetic counselling as a routine step, not something that waits for other signals.
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Family history is still taken, but is not the deciding factor
Even with an entirely unremarkable family history, the rarity of the cancer itself is usually reason enough to test.
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Testing looks at the specific gene linked to that cancer
The counsellor already knows which gene or small group of genes to start with, because the cancer type points there directly.
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A confirmed fault opens up wider screening
Several of these syndromes raise risk across more than one organ, so a positive result usually leads to a specific, ongoing screening plan rather than a one-off check.
Words on your report
Terms that come with a rare-cancer diagnosis
- Syndrome
- A recognised pattern of several linked health conditions caused by one inherited fault, rather than a single isolated finding.
- Penetrance
- How often a fault actually leads to cancer among carriers. For some of these syndromes it is unusually high.
- Tumour suppressor gene
- A gene whose normal job is to stop cells growing out of control. Many rare inherited cancer syndromes involve a fault in this type of gene.
- Surveillance protocol
- A structured, ongoing schedule of scans and checks designed specifically for people known to carry a particular fault.
- Genetic counsellor
- The specialist who confirms which gene to test for and explains the surveillance plan that follows a positive result.
- Multidisciplinary team
- The group of specialists across different organs who jointly manage someone with a syndrome affecting more than one part of the body.
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Side by side
A common cancer, versus one of these rare cancers
A common cancer type
One of these specific rare cancers
Testing usually depends on age and family history
Testing is usually offered regardless of family history
Many possible genes could be involved
The cancer type itself points to a specific gene
Referral criteria are relatively strict
Referral criteria are deliberately relaxed
A negative result is common and expected
A positive result is found more often than with common cancers
Being straight with you
Does a rare-cancer diagnosis always mean an inherited fault?
No. Even within this group, a meaningful share of people are found to have no inherited fault after testing. What makes these cancers different is not certainty — it is that the odds of finding a fault are high enough that testing everyone makes sense, rather than only testing people who also have a striking family history.
This vertical is about inherited faults, not the tumour itself
Genetic counselling for cancer looks at faults present in every cell of your body, inherited or arising for the first time in you. Testing done on the tumour tissue alone, to guide treatment choices, is a separate process handled by your oncology team.
What this page cannot tell you
It cannot tell you whether your own diagnosis carries an inherited fault. That depends on the exact cancer type, your age, and sometimes features seen only under a microscope — details a genetic counsellor needs to review directly.
If your diagnosis is on this list and nobody has mentioned genetic testing, ask about it at your next appointment.Commonly believed
What families get wrong about rare cancer diagnoses
"It's so rare, it must just be bad luck, not genetics."
For this specific group of cancers, rarity is actually the reason genetics is suspected more, not less. A large share of cases in this group do carry an identifiable inherited fault.
"If it were genetic, other relatives would already have had it."
Some of these syndromes are severe enough, or the gene faults rare enough, that a family can go generations without a second case, or the fault can appear for the first time in one person.
"Testing for a rare cancer only tells you about that one cancer."
Several of these syndromes raise risk across more than one organ. A positive result often changes screening for organs that have nothing to do with the original diagnosis.
"My child is too young to be tested."
For syndromes where childhood screening genuinely changes outcomes, testing children is standard practice, not something that waits until adulthood.
Questions we are asked
Common questions about rare cancers and genetic testing
My diagnosis is rare but not on this list. Should I still ask about testing?
Yes. This list covers only the clearest, best-known patterns. Other rare cancers can still be worth discussing with a genetic counsellor, especially alongside a notable age or family history.
Does having one of these cancers mean I definitely have an inherited fault?
No. A meaningful share of people with these cancers test negative. What sets this group apart is that the odds of finding a fault are high enough to justify testing everyone, not that testing always finds one.
Will testing delay my treatment?
Usually not. Genetic testing is normally arranged alongside treatment planning rather than instead of it, and your oncology team will tell you if a result is needed before a specific treatment decision.
My child has one of these cancers. Do I need to be tested too?
Usually the child is tested first. If a fault is found, parents are then offered testing to see which of them carries it, and whether it arose for the first time in the child.
What does a positive result change for me?
It usually leads to a structured, ongoing surveillance plan covering every organ the syndrome affects, not just the one already diagnosed. Your counsellor will set this out clearly.
Is this the same as testing my tumour for treatment purposes?
No. This is inherited testing, looking at every cell in your body. Testing the tumour tissue itself, to choose a treatment, is a separate process your oncology team manages directly.
What sample is needed?
A blood sample is normally enough for the inherited test. Saliva is sometimes used instead, depending on the laboratory.
Where do I start?
Ask your treating oncologist whether a genetic referral has already been arranged. If you are unsure, call the CION helpline and name the exact diagnosis.
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)
Medical Oncologist
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Sources
- GeneReviews (NCBI) — RB1-Related Retinoblastoma
- GeneReviews (NCBI) — Li-Fraumeni Syndrome
- GeneReviews (NCBI) — Hereditary Paraganglioma-Pheochromocytoma Syndromes
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
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
Cancer in both breasts, both kidneys or both eyesBilateral retinoblastoma is one of the clearest examplesCancer at a young age: when it points to a geneSeveral of these cancers matter most in childrenTesting criteria explained without the jargonSee the full list of what counts, in plain languageWhat if no affected relative is alive to test?Relevant when the rare-cancer diagnosis was in a relative who has since died
Talk to us
Diagnosed with a rare cancer and unsure about testing?
Tell us the exact diagnosis and we will tell you honestly whether a genetic referral is standard for it. One helpline serves every CION centre.