Medical Oncologist
CION Cancer Clinics
Cancer genetics: what it means and why it matters | CION Cancer Clinics
Most cancer is not inherited. It comes from faults that build up in one person's cells over a lifetime. A smaller group of cancers start with a fault that was already there at birth and can be passed down a family. This page explains the difference, what an inherited fault actually does, and when it is worth asking your doctor about testing. 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
- What does cancer genetics actually mean?
- Sporadic, familial, hereditary: what each one means
- Why an inherited fault does not mean cancer is certain
- The words you will meet, in plain language
- What a result changes, and what it does not
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about cancer and genes
The short answer
What does cancer genetics actually mean?
Cancer genetics is the study of the instructions inside your cells and what happens when one of those instructions is faulty. Most cancers are caused by faults that build up in one person's body over a lifetime. A small share are caused by a fault that was already present at birth, in every cell, passed down from a parent.
Two different kinds of gene fault
The first kind happens in one organ, in one person, usually later in life. It is not in the rest of the body and it cannot be passed to a child. The second kind is inherited. It sits in every cell, including the egg or sperm cells, which is how it travels from one generation to the next. Genetic testing in cancer care is usually asking which of these two you are dealing with.
Why anyone bothers to ask
The answer changes real decisions. It can change the treatment offered to the person who already has cancer, and when scans start for a brother or a daughter who is perfectly well. It also closes the question for relatives who assumed they were next, which is the most common outcome and the one nobody expects.
A gene fault is not a diagnosis. It is a statement about risk.The three words you will hear
Sporadic, familial, hereditary: what each one means
Doctors use these three words very precisely, and families often use them to mean the same thing. They do not.
Sporadic
The cancer arose from faults that built up in one organ during that person's life. Nobody passed anything on and nobody will inherit anything. This is what most cancer is.
Usually looks like
- One person in the family affected
- Diagnosed at an older age
- One cancer, in one organ
Familial
More cancer in the family than you would expect, but testing finds no single faulty gene behind it. Shared habits, shared surroundings and many small genetic differences acting together can all produce this pattern.
Familial does not mean the testing failed. It means the answer is not one gene.Hereditary
A single faulty gene, present from birth, is driving the risk. It can be identified by a test, and relatives can be tested for that exact fault rather than being screened blindly.
Often looks like
- Cancer at an unusually young age
- Several close relatives, often on one side
- Two separate cancers in one person
- Rare cancers, or breast cancer in a man
Why the label matters
Only the third group has a fault relatives can be tested for. The middle group is still watched closely, but from the family history rather than from a result.
Not sure whether this applies to you?
Ask an oncologistHow a fault turns into a cancer
Why an inherited fault does not mean cancer is certain
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You carry two copies of every gene
One came from your mother and one from your father. For most of the genes involved in inherited cancer, one working copy is enough to keep the cell behaving normally.
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An inherited fault knocks out one copy from the start
Someone who inherits a fault is born with one working copy instead of two, in every cell of the body. Nothing is wrong yet. The cell still has a working instruction to follow.
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The second copy can be damaged during life
Ordinary wear, copying errors when cells divide, and things like tobacco smoke can damage the remaining copy in a single cell. Now that one cell has no working instruction.
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That one cell can begin to grow unchecked
With the brake gone, that cell can divide when it should not. Usually the body clears it. Occasionally it does not, and a tumour forms.
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Which is why risk is not certainty
The inherited fault only supplies the first step. Whether the second step happens is partly chance, which is why two sisters carrying the same fault can have very different lives.
On your report
The words you will meet, in plain language
- Gene
- One instruction in the body's manual. Genes tell cells when to grow, when to stop and how to repair themselves.
- Variant
- A spelling difference in that instruction. Most variants are harmless and simply make people different from each other.
- Pathogenic variant
- A spelling difference known to break the instruction. This is what people mean when they say a gene fault or a mutation.
- Carrier
- Someone who has an inherited fault but does not have cancer. A carrier is not a patient and does not need treatment.
- Penetrance
- How often a fault actually leads to cancer across everyone who carries it. It is never all of them, and it differs from gene to gene.
- Germline
- Present in every cell from birth, and therefore inheritable. The opposite word is somatic, meaning a fault found only inside the tumour.
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Side by side
What a result changes, and what it does not
A fault is found
No fault is found
Relatives can be tested for that exact fault
Relatives are watched using the family history instead
Scans may start earlier, and may include extra tests
Routine screening for age and background applies
Some treatment options may open up
Treatment is planned on the tumour itself
Family planning choices can be discussed
Nothing specific can be offered to test for
Commonly believed
Four things families tell us, and what is actually true
"There is no cancer on my mother's side, so it cannot be inherited."
A fault can come from either parent and behaves the same way whichever side it came from. A man can carry and pass on a fault linked to breast and ovarian cancer without ever being ill himself.
"Nobody in our family had cancer, so testing is pointless."
A fault can appear for the first time in one person, and small families simply do not have enough relatives for a pattern to show. Many people found to carry a fault have a family history that looks completely unremarkable.
"If the test is positive, I will definitely get cancer."
It raises risk. It does not settle the matter. Many carriers never develop cancer, and those who do are often found early because they were being watched.
"It skipped a generation, so it has left our family."
Genes do not skip. What skips is the illness. A parent can carry a fault, never develop cancer, and pass it to a child who does. From the outside that looks like a generation was missed, but the fault was there the whole time.
Being straight with you
What this page cannot tell you
It cannot tell you whether your family carries a fault. That question is answered by a genetic counsellor who has drawn out your family tree, asked who was diagnosed and at what age, and in most cases arranged a test for the relative who already has cancer. Nothing you read online can stand in for that conversation.
It cannot interpret a report you are holding
Genetic reports are written for the doctor who ordered them. The same gene name can mean very different things depending on the exact variant and how it is classified. If you have a report in your hand, bring it to someone qualified to read it rather than searching for the variant online.
Who this does not apply to
Most people reading this do not need a genetic test. If your family has one relative diagnosed at an older age, and no pattern of young diagnoses or rare cancers, testing is unlikely to change anything for you. A counsellor is as willing to tell you that as to recommend a test.
If you are unsure whether your family history counts, call the helpline and describe it. Someone will tell you honestly whether it is worth a referral.Questions we are asked
Common questions about cancer and genes
Does having cancer in the family mean I will get it?
No. Most cancer in most families is not inherited, and even a confirmed gene fault raises risk rather than settling anything. What family history does is tell your doctor whether you should be watched earlier or more closely than other people your age.
Can a man carry a breast cancer gene fault?
Yes, and he can pass it to a daughter or a son in exactly the same way a woman can. He also carries a raised risk himself, including of prostate and male breast cancer. Leaving men out of the family tree is one of the most common reasons an inherited pattern is missed.
Who in the family should be tested first?
Wherever possible, the relative who already has cancer. Testing that person first tells you whether there is a fault to look for at all. If they test negative, testing well relatives usually adds nothing.
Is a blood test enough, or do they need tissue?
For inherited testing a blood sample is normally enough, and saliva is sometimes used. Tissue from a tumour answers a different question about the cancer itself. If the relative who had cancer has died, a stored tissue block from their old surgery can sometimes still be tested.
My result says variant of uncertain significance. What now?
It means the laboratory found a spelling difference and does not yet know whether it matters. It is not a positive result and should not change your treatment or lead to preventive surgery. Classifications are reviewed as evidence grows, so ask how you will be told if it is ever reclassified.
Should my children be tested?
For faults that raise risk only in adult life, testing usually waits until the child is an adult and can decide for themselves. A small number of syndromes do need childhood testing, because screening starts young and genuinely helps. Your counsellor will tell you which situation you are in.
Will a test result affect my insurance?
India has no dedicated law on genetic discrimination in insurance, and the position has been argued in court rather than settled by statute. It is a fair question to raise with your counsellor before testing, not afterwards, and it is one reason some people arrange cover first.
Where do I start if I think my family history is unusual?
Write down who was diagnosed, with what, and at roughly what age, on both sides. Take that list to a genetic counsellor or to your oncologist. Call the CION helpline if you are not sure 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)
Medical Oncologist
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Sources
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- Cancer Research UK — Inherited cancer genes and increased cancer risk
- NHS — Predictive genetic tests for cancer risk genes
- MedlinePlus Genetics — What does it mean to have a genetic predisposition to a disease?
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
Are genes the same as DNA and chromosomes?The vocabulary, before anything elseSporadic, familial and hereditary cancerThe three patterns, told apart properlyShould you have genetic testing?A plain check of whether your family history qualifiesWhat a genetic counsellor doesWho you actually see, and what happens in the room
Talk to us
Not sure whether your family history counts?
Tell us who in your family was diagnosed and at what age. We will tell you honestly whether a genetic referral is worth making, and arrange it if it is. One helpline serves every CION centre.