Medical Oncologist
CION Cancer Clinics
Tumour-only testing and the risk of missing an inherited cause | CION Cancer Clinics
A tumour test looks for faults inside the cancer to guide treatment. It is not designed to tell you whether a fault was inherited, and it can miss one completely. If your family history or your type of cancer points to an inherited cause, a separate blood test is usually still needed. This page explains how that happens and what to ask your oncologist. 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
- Can a tumour test miss an inherited cancer gene?
- How does an inherited fault slip through a tumour test?
- What should happen after a tumour-only result?
- What do the words on a tumour report mean?
- Tumour test or blood test: what can each one answer?
- What this page cannot tell you
- Four things families assume about tumour results
- Common questions about tumour-only testing
The short answer
Can a tumour test miss an inherited cancer gene?
Yes. A tumour-only test reads the DNA of the cancer alone, with nothing from your healthy cells to compare it against. It is built to find faults that guide treatment, not to decide whether a fault was there from birth. So an inherited fault can be missed, filtered out, or printed on the report without anyone saying it might run in the family.
What the tumour test was designed for
Tumour testing, sometimes called tumour profiling, looks for somatic changes, meaning faults found only inside the cancer. Its job is to match the cancer to a targeted medicine. That work belongs to your treating oncologist and is covered on our targeted therapy pages. The question of inheritance needs a different test, done on blood or saliva.
Why this matters to the family
An inherited fault sits in every cell and can pass to children, brothers and sisters. If it is missed, relatives lose the chance to be tested for that exact fault and to start screening early. The person with cancer may also miss a treatment choice that depends on knowing the fault came from birth.
A clear tumour report is a statement about the tumour. It is not a statement about your family.Four ways it happens
How does an inherited fault slip through a tumour test?
None of these is a laboratory error. Each one follows from what the tumour test was built to do.
It is filtered out on purpose
Many tumour-only reports remove changes that look inherited, because the lab's task is to report what is new in the cancer. A real inherited fault can be treated as background and never appear on the page you are handed.
It is found but not labelled
The report may list a fault in BRCA1 or in a Lynch syndrome gene without saying whether it was there from birth. If nobody asks, it is read as a tumour change and the family is never referred.
The gene is not on the panel
Tumour panels are chosen for treatment. Genes that matter for inheritance may be left out, or read only in part.
Commonly missed
- Genes with no targeted medicine attached
- Large deletions that remove a whole section of a gene
- Stretches of DNA the tumour test reads poorly
The sample was small or old
A tiny biopsy, or a tissue block stored for years, can give a weak reading. A fault can be missed simply because there was not enough good DNA to read.
Not sure whether this applies to you?
Ask an oncologistAfter a tumour report
What should happen after a tumour-only result?
Check the report for an inherited flag
Some labs add a line saying a finding may be germline, meaning present from birth. Ask your oncologist whether your report carries that line and what it refers to.
Look at the family history on its own
A tumour report never replaces the family tree. Cancer at a young age, several relatives on one side, or a rare cancer are reasons to ask for a blood test whatever the tumour showed.
Confirm any flagged fault on blood
A fault seen in the tumour is confirmed as inherited only by testing blood or saliva. Nobody should start testing relatives from a tumour report alone.
See a genetic counsellor before and after
The counsellor chooses which genes to test on blood, explains the result, and writes the letter your relatives will need. Counselling in Telugu can be arranged if you ask.
On your report
What do the words on a tumour report mean?
- Tumour-only testing
- DNA is read from the cancer alone, with no sample of healthy cells beside it. It is the most common kind of tumour test.
- Paired testing
- The tumour and a blood sample are read together. A fault in both is likely inherited. A fault only in the tumour is likely acquired.
- Somatic
- A fault found only inside the tumour. It developed during life and cannot be passed to a child.
- Germline
- A fault present in every cell from birth. It can come from a parent and pass to a child.
- Variant allele frequency
- How much of the DNA read carries the fault. A very high share can hint that a fault was inherited, but it cannot prove it.
- Possible germline finding
- A note from the lab that a fault may be inherited. It is a prompt to test blood, not a result in itself.
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Side by side
Tumour test or blood test: what can each one answer?
Tumour-only test
Blood test for inherited faults
Finds faults that guide targeted medicines
Finds faults that were present from birth
Needs tissue from a biopsy or surgery
Needs only a blood or saliva sample
Cannot reliably say whether a fault is inherited
Tells you whether relatives can be tested
A clear result says nothing about the family
A clear result in the affected relative helps the whole family
Ordered by the treating oncologist
Usually arranged with a genetic counsellor
Being straight with you
What this page cannot tell you
It cannot tell you whether a fault on your report is inherited. Only a blood test, read with a genetic counsellor, can answer that. What your specific variant means is a question for the counsellor who ordered the test.
It cannot judge your tumour report
Reports from different labs are laid out differently. Some filter out inherited faults, some flag them and some say nothing at all. Your oncologist knows which kind of report you hold and what was and was not looked at. Labs do not yet agree on one way to flag a possible inherited finding, and the studies comparing approaches are still growing.
Who this does not apply to
Most people who have tumour testing do not need a separate blood test. If the cancer came at an older age, nobody else in the family is affected and the report raises no flag, a blood test may add nothing. Your oncologist will tell you plainly if that is your situation.
If the tumour report is the only test your family has had, ask one question at the next visit: does anything here need confirming on blood?Commonly believed
Four things families assume about tumour results
"The tumour test was normal, so the cancer is not inherited."
The tumour test was not built to answer that. A family can carry an inherited fault the tumour report never shows, because it was filtered out or because the gene was not tested.
"The report shows a BRCA fault, so my daughter has it too."
Not necessarily. The fault may have developed only in the cancer. A blood test on the person with cancer shows whether it was inherited, and only then does testing the daughter make sense.
"We already paid for the expensive test. Another one is a waste."
The two tests answer different questions. One blood result in the person with cancer can guide testing for every relative who follows, which is where most of its value lies.
"If it were inherited, the oncologist would have told us."
Oncologists read tumour reports for treatment choices. An inherited finding can sit in the small print or not be reported at all. Asking the question directly is reasonable, and good doctors welcome it.
Questions we are asked
Common questions about tumour-only testing
Can a tumour test tell if my cancer is inherited?
Not reliably. It reads the tumour alone, so it cannot tell whether a fault began in the cancer or was there from birth. Some reports flag a possible inherited finding, but that flag is only a prompt. A blood test is what settles the question for you and your family.
What is paired tumour and blood testing?
The lab reads the tumour and a blood sample side by side. A fault found in both is likely inherited, and one found only in the tumour is likely acquired. It lowers the chance of missing an inherited cause, though it may not cover every gene a counsellor would choose.
My tumour report mentions BRCA2. Should my sister be tested?
Not yet. First, the person with cancer should have a blood test to see whether that BRCA2 fault is inherited. If it is, your sister can be tested for that exact fault. If it is not, her risk is judged from the family history instead.
Which cancers make an inherited cause more likely?
Ovarian, pancreatic and male breast cancer, some bowel and womb cancers, and any cancer at an unusually young age. In these situations a blood test is often offered whatever the tumour showed. Your oncologist or counsellor will tell you whether your situation is one of them.
The biopsy tissue has run out. Can we still check for an inherited fault?
Yes. An inherited fault is in every cell, so a blood or saliva sample is enough and no tumour tissue is needed. This is one real advantage of testing blood when the tumour sample was small or has been used up by earlier tests.
Will a blood test change my treatment?
Sometimes. For a few cancers, an inherited fault in a gene like BRCA1 or BRCA2 opens up specific medicines or changes surgical choices. Your oncologist will say whether a result could change your plan. Even when it does not, it matters for your relatives.
Does Aarogyasri or Ayushman Bharat pay for the blood test?
Cover for genetic tests varies by scheme, by hospital and over time, so nobody can promise it in advance. Ask the insurance desk before testing, with the exact name of the test. The CION helpline can tell you which papers to bring.
Who should I ask about my tumour report?
Start with the oncologist who ordered it. If a possible inherited finding is mentioned, or your family history looks unusual, ask for a referral to a genetic counsellor. Call the CION helpline if you are unsure who to approach, and someone will point you to the right clinic.
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
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- National Cancer Institute — Biomarker Testing for Cancer Treatment
- National Cancer Institute — Genetics of Breast and Gynecologic Cancers (PDQ) - Health Professional Version
- MedlinePlus Genetics — What do the results of genetic tests mean?
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
When a tumour result triggers a germline testThe findings that should send you for a blood testWhy one test does not replace the otherTwo tests, two different questionsHaving both tests at the same timeWhen paired testing avoids a second waitWho orders which testOncologist or geneticist, and who to ask first
Talk to us
Had a tumour test but no blood test?
Tell us what the tumour report says and who in your family has had cancer. We will tell you honestly whether a genetic referral is worth making. One helpline serves every CION centre.