Medical Oncologist
Genetic risk & family testing
Somatic Mutation Found on NGS: — Could It Be Inherited?
Tumour testing done to guide your cancer treatment sometimes finds mutations that could be inherited. Whether they are changes everything that comes next — for you and for your family.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed August 2026
- Not all somatic labels are final — Tumour-only NGS cannot reliably separate mutations that arose in the cancer from ones you were born with.
- Certain genes raise the question immediately — Mutations in BRCA1, BRCA2, or the Lynch syndrome genes carry a meaningful chance of being inherited even when called somatic.
- A blood test gives the definitive answer — Germline testing on a blood or saliva sample is the only way to confirm whether a mutation is inherited.
- The answer matters for your family — A confirmed inherited mutation means first-degree relatives can be offered testing and, if positive, surveillance that can prevent cancer.
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A mutation called 'somatic' on tumour-only NGS testing may still be a germline — that is, inherited — variant. Tumour-only sequencing cannot reliably tell the two apart. NCCN and ESMO recommend confirmatory germline testing when certain high-risk gene mutations appear on a tumour report, regardless of how they were initially classified.
Why does tumour testing flag mutations that might be inherited?
Most NGS panels used in cancer treatment sequence only tumour tissue. Without a matched normal sample — blood or saliva from the same person — the laboratory cannot directly compare tumour DNA against your inherited DNA to see which variants were already present at birth.
Instead, labs use indirect signals: the proportion of tumour cells carrying the variant, and whether the variant appears in databases of known inherited mutations. These signals are useful but not definitive. A meaningful proportion of variants labelled 'somatic' turn out to be germline when a separate blood test is done.
This is not a laboratory error. It is a known limitation of tumour-only testing, and NCCN, ASCO, and ESMO guidelines all account for it by recommending germline follow-up in specific situations.
Which mutations found on tumour testing most often turn out to be inherited?
BRCA1 and BRCA2 mutations found in breast, ovarian, pancreatic, or prostate cancer have a substantial chance of being germline rather than somatic. The same applies to mutations in the Lynch syndrome genes — MLH1, MSH2, MSH6, and PMS2 — found in colorectal, endometrial, gastric, or ovarian cancer.
Other genes where germline follow-up is routinely recommended include PALB2, ATM, CHEK2, and TP53, depending on cancer type and family history. Your oncologist or genetic counsellor will tell you whether the specific variant in your report falls into a category where follow-up is advised.
The threshold for recommending germline testing is not whether a mutation is definitely inherited. It is whether the possibility cannot be responsibly excluded.
What do the words on your test report actually mean?
- Somatic mutation
- A mutation that arose in a specific cell during your lifetime and is present only in the tumour. It was not inherited and cannot be passed to your children.
- Germline mutation
- A mutation present in every cell in your body from birth, inherited from a parent. It can be passed to children, and your first-degree relatives may also carry it.
- Tumour-only NGS
- Sequencing done on tumour tissue alone, without a matched blood sample. It is designed to guide treatment, not to assess inherited risk, and cannot definitively classify a mutation as somatic or germline.
- Paired (germline) testing
- Sequencing done on blood or saliva from the same person. It directly compares tumour DNA against your constitutional DNA and can confirm whether a variant is inherited.
- Variant of uncertain significance (VUS)
- A mutation found in your DNA where the evidence is not yet strong enough to classify it as harmful or harmless. Most VUS findings are eventually reclassified as more data accumulates. A VUS is not a diagnosis.
- Hereditary cancer syndrome
- A recognised pattern of elevated cancer risk caused by an inherited mutation in a specific gene — such as BRCA-related breast and ovarian cancer syndrome, or Lynch syndrome.
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What happens next after a concerning mutation is flagged?
Your oncologist flags the finding
Your treating oncologist reviews the NGS report and identifies variants that warrant germline follow-up, based on the gene involved, your cancer type, and your family history.
Referral to a genetic counsellor
You are referred to a certified genetic counsellor who reviews your personal and family history, explains what the tumour finding means, and recommends whether germline testing is appropriate.
Germline testing on blood or saliva
A blood draw or saliva swab is sent for germline testing. This looks at your constitutional DNA — the DNA you were born with — rather than the tumour.
Result and classification
Results typically take two to four weeks. The variant is classified as pathogenic, likely pathogenic, a variant of uncertain significance, or negative. Your genetic counsellor explains what the classification means for you.
Cascade testing for family members
If your result is pathogenic or likely pathogenic, your genetic counsellor will help you understand who in your family should be offered testing — typically parents, siblings, and children over 18.
If the mutation is germline, what does that mean for you and your family?
A confirmed germline mutation changes your own surveillance and opens the door to testing for first-degree relatives. For family members who test positive and do not yet have cancer, surveillance can detect problems early — or prevent them altogether. That is the clinical point of the whole process.
For BRCA1 and BRCA2 carriers, NCCN guidance recommends annual breast MRI and mammogram from around age 25–30, and clinical breast examination every six to twelve months. NCCN reports lifetime breast cancer risk in the range of 50–72% for BRCA1 carriers and 45–69% for BRCA2 carriers. Ovarian cancer lifetime risk is reported at around 44% for BRCA1 and around 17% for BRCA2. These figures apply to carriers — not to family members who test negative.
For Lynch syndrome gene carriers, NCCN recommends colonoscopy every one to two years from around age 20–25. Lifetime colorectal cancer risk for MLH1 and MSH2 carriers is reported by NCCN to be in the range of 40–80%; for MSH6 and PMS2 carriers, substantially lower. For women, annual endometrial assessment is recommended from around age 30–35.
Your own surveillance plan depends on your age, the specific gene, and your personal and family history. The schedules above are starting points your genetic counsellor will adapt to you.
What else do families need to know after getting these results?
The germline test came back negative — what does that mean?
A negative germline result means the variant in your tumour is almost certainly somatic — it arose in the cancer and is not present in your other cells. That is reassuring for your family, because they did not inherit it from you. It does not change your cancer diagnosis or treatment, but it does mean relatives are unlikely to have elevated risk from this specific mutation. Ask your oncologist whether any other hereditary risk factors still apply given your family history.
My result was a VUS — should I be worried?
A variant of uncertain significance means the evidence is genuinely incomplete, not that the variant is probably harmful. The majority of VUS findings are eventually reclassified as benign as more data accumulates. Your genetic counsellor will not recommend major preventive interventions on the basis of a VUS alone. Do not make irreversible decisions — such as preventive surgery — based on a VUS result. Laboratories actively update their classifications, and your counsellor should re-contact you if yours changes.
Should my children be tested now?
For most adult-onset hereditary syndromes — BRCA1/2, Lynch syndrome — ASCO and ESMO recommend waiting until around age 18, when a young person can make an informed decision. This is not delay for its own sake: a result a child is not ready to understand cannot help them. Testing is generally considered earlier only when a specific mutation causes childhood cancer risk, which your genetic counsellor will tell you if that applies. Your counsellor can also give you language to prepare your children as they approach adulthood.
Does a germline mutation change my cancer treatment?
It can, and this is one reason germline testing matters even during active treatment. Confirmed germline BRCA1 or BRCA2 mutations may open eligibility for PARP inhibitor therapy in breast, ovarian, pancreatic, and prostate cancers. Lynch syndrome gene mutations are relevant to decisions about immunotherapy. Your oncologist will review the germline result specifically for treatment implications and coordinate with your genetic counsellor.
How do I tell my siblings and parents they may need testing?
Your genetic counsellor will usually offer you a letter you can give to family members, written in plain language, explaining the finding and suggesting they speak to their own doctor. You are not obligated to tell anyone, and how you share this information is entirely your choice. What relatives do with it is also their decision. Many people find it easier to hand over the letter than to explain it themselves, especially when the conversation is emotionally difficult.
Is germline testing available in India, and what does it cost?
Germline testing is available at accredited molecular diagnostics laboratories across India. Cost varies considerably by the panel ordered — a targeted single-gene test is substantially less expensive than a broad multi-gene panel — and by laboratory. Any figure is indicative and changes over time. Your genetic counsellor will recommend the most appropriate test for your situation rather than a broad panel you may not need. CION can coordinate germline testing through accredited partner laboratories; ask your treating team or genetic counsellor at your centre.
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Common questions
Frequently asked questions
What does 'somatic mutation' mean in plain language?
A somatic mutation arose inside a cell at some point during your lifetime — often because of copying errors as cells divide, or because of environmental exposure. It is present only in cells descended from that original altered cell, not in your blood, eggs, or sperm. It cannot be inherited by your children. The majority of mutations found on tumour NGS are somatic.
How likely is it that my 'somatic' BRCA mutation is actually germline?
The proportion varies by gene, cancer type, and the specific features of the variant. For BRCA1 and BRCA2 mutations found on tumour-only NGS in ovarian cancer, published series have reported that a meaningful proportion — in some studies one in five or more — turn out to be germline on follow-up blood testing. The figure differs for other genes and cancer types. This is why NCCN and ASCO do not rely on the tumour label alone when one of these high-risk genes is involved.
Do I have to do germline testing if my oncologist recommends it?
No. Germline testing is voluntary. Your oncologist and genetic counsellor will explain what the test could show and how the result might affect your treatment and your family, but the decision is yours. Some people choose to wait; some choose not to test at all. Your treating team will respect that choice. The information is available to you whenever you are ready.
I have a family history of cancer — does that make it more likely the mutation is germline?
Yes. Multiple relatives with the same cancer type, or relatives diagnosed at young ages, raises the probability that a mutation found on tumour testing is inherited rather than acquired. Your genetic counsellor will take your full family history into account when recommending whether and what to test. Even without a clear family history, certain genes and cancer types make germline testing worthwhile, because some hereditary mutations arise without an obvious family pattern.
If the mutation is germline, does every sibling definitely have it?
No. An inherited mutation is passed from parent to child with roughly a fifty percent chance at each transmission — the same odds as a coin toss. On average, half of your siblings will have inherited it and half will not. The only way to know which is which is individual germline testing. A sibling who tests negative does not carry the mutation and does not face elevated risk from it. A sibling who tests positive can then act on that information — which is the value of cascade testing.
What is the difference between tumour testing for treatment and genetic testing for family risk?
Tumour testing — the NGS panel used in your cancer care — is designed to find variants that predict how the tumour will behave and what drugs it may respond to. It sequences tumour tissue. Germline testing is designed to find inherited variants in your constitutional DNA, using blood or saliva, and to classify them according to whether they cause hereditary cancer risk. The two tests have different purposes and different samples, and report results in different ways. Finding a variant on tumour testing is the starting point, not the answer — the answer comes from the germline test.