Medical Oncologist
CION Cancer Clinics
The ATM gene: what it does and why it matters | CION Cancer Clinics
ATM is a gene that helps cells notice and repair broken DNA. A faulty copy inherited from a parent raises the lifetime chance of breast cancer, and possibly pancreatic and prostate cancer, but far less than BRCA1 or BRCA2 does. This page explains what the gene does, how a fault leads to risk, and why one faulty copy is not the same as the childhood illness ataxia-telangiectasia. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
NG
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
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
On this page
- What does the ATM gene actually do?
- Is an ATM fault the same as ataxia-telangiectasia?
- How does a faulty ATM copy lead to cancer?
- What do the words on an ATM report mean?
- How is ATM different from BRCA1 and BRCA2?
- What this page cannot tell you
- What do families get wrong about ATM?
- Common questions about the ATM gene
The short answer
What does the ATM gene actually do?
ATM is a gene that acts like an alarm for damaged DNA. When the DNA inside a cell breaks, the ATM instruction tells the cell to stop, repair the break, or shut itself down if the damage is too great. Everyone has two copies of ATM, one from each parent.
Why a faulty copy matters
If one copy is faulty from birth, the alarm still works, but it has no spare. Over a lifetime, a cell that loses the second copy can keep dividing with broken DNA. That is how an ATM fault raises the chance of some cancers, most clearly breast cancer, and to a lesser degree pancreatic and prostate cancer.
A moderate-risk gene, not a high-risk one
Doctors group ATM with the moderate-risk genes. The rise in breast cancer risk is real but smaller than with BRCA1 or BRCA2. That changes the plan. Carriers usually need closer screening, not dramatic surgery, and the family history often shapes the advice as much as the result does.
Carrying one faulty ATM copy is not a diagnosis. It is a statement about risk.One gene, two conditions
Is an ATM fault the same as ataxia-telangiectasia?
No. Families often confuse the two, and the difference matters a great deal.
One faulty copy
This is what almost every adult with an ATM result has. The person is healthy, has no symptoms and usually learns about it only through a cancer gene test. The main effect is a raised lifetime risk of breast cancer.
Usually means
- No illness from the fault itself
- Closer breast screening for women
- A conversation about relatives
Two faulty copies
A child who inherits a faulty copy from both parents has a rare condition called ataxia-telangiectasia, or A-T. It affects balance and movement from early childhood, weakens the immune system and makes the body very sensitive to radiation.
A-T is diagnosed in childhood by a neurologist. It is not something an adult carrier suddenly develops.Why this matters in India
When parents are related by blood, such as cousins or uncle and niece, both are more likely to carry the same fault. A carrier planning a family within the community can ask whether a partner should be tested too.
What it does not do
One faulty copy does not cause ataxia, weak immunity or illness in the carrier. If you feel well, the result has not made you unwell. It has told you something about the future.
Not sure whether this applies to you?
Ask an oncologistFrom fault to risk
How does a faulty ATM copy lead to cancer?
-
DNA breaks every day
Ordinary life breaks DNA. Cell division, sunlight, tobacco smoke and normal body chemistry all cause small breaks that must be fixed.
-
ATM raises the alarm
ATM senses a break in both strands of the DNA. It pauses the cell and calls in the repair teams, including the proteins made by BRCA1 and BRCA2.
-
A carrier has one working alarm
With one faulty copy from birth, each cell relies on the single working copy. For most of life this is enough, and the cell behaves normally.
-
The second copy can be lost in one cell
Chance damage can knock out the working copy in a single breast or pancreas cell. That cell no longer stops for broken DNA.
-
Risk rises, but it is not certain
Most carriers never develop cancer. The fault supplies one step, and whether the rest follows depends on chance, hormones, habits and other genes.
On your report
What do the words on an ATM report mean?
- ATM
- Short for ataxia-telangiectasia mutated, the gene named after the childhood condition it causes when both copies are faulty.
- Heterozygous
- One faulty copy and one working copy. This is the usual adult carrier result.
- Pathogenic variant
- A spelling change in the gene known to break the instruction. Likely pathogenic is treated the same way in practice.
- Variant of uncertain significance
- A change the laboratory cannot yet classify. It should not change your screening or treatment on its own.
- Germline
- Present in every cell from birth, so it can be passed on. A fault found only in a tumour is called somatic.
- Penetrance
- How often a fault actually leads to cancer across all carriers. For ATM it is moderate, and it varies between families.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Side by side
How is ATM different from BRCA1 and BRCA2?
ATM carrier
BRCA1 or BRCA2 carrier
Moderately raised breast cancer risk
Much higher breast cancer risk
Ovarian risk is not clearly raised
Ovarian risk is clearly raised
Preventive mastectomy is rarely advised on the gene alone
Preventive surgery is commonly discussed
Family history carries a lot of weight in the plan
The gene result drives most of the plan
Being straight with you
What this page cannot tell you
It cannot tell you what your own ATM variant means. Some ATM changes behave more strongly than others, and the evidence on individual variants is still growing. What your specific variant means is a question for the counsellor who ordered the test.
It cannot set your screening plan
Your plan depends on your age, your family history, your breast density and whether you have already had cancer. Two carriers of the same fault can reasonably be given different advice.
Who this does not apply to
Most people do not need an ATM test. If nobody in your family has had breast, pancreatic or prostate cancer at a young age, and no relative has a known fault, testing is unlikely to help you. Tumour testing for treatment is a different test, covered under targeted therapy.
Commonly believed
What do families get wrong about ATM?
"An ATM fault means I will get ataxia too."
No. Ataxia-telangiectasia needs two faulty copies and starts in early childhood. An adult carrier with one copy does not develop it.
"It is a breast cancer gene, so it only matters for women."
Men carry and pass on ATM faults equally. A man with a fault may also face a raised risk of prostate and pancreatic cancer.
"ATM is as serious as BRCA, so I need the same surgery."
The risk is lower than with BRCA. Most ATM carriers are offered closer screening instead, and surgery is weighed against the family history.
"Carriers can never have radiotherapy or X-rays."
For carriers of one copy, current guidance does not forbid radiotherapy or mammograms. Extreme radiation sensitivity belongs to people with two faulty copies.
Questions we are asked
Common questions about the ATM gene
Is ATM a cancer gene?
It is a gene that protects against cancer when it works. A faulty copy weakens that protection, which is why it appears on inherited cancer panels. It is grouped with the moderate-risk genes, below BRCA1 and BRCA2 in how much it raises breast cancer risk.
Which cancers are linked to ATM?
The clearest link is breast cancer in women. Pancreatic cancer and prostate cancer are also linked, though the evidence is less settled. Your counsellor will look at the cancers in your own family to decide which checks make sense for you.
How did I get an ATM fault?
Almost always from one parent, who may never have had cancer. It is present from birth in every cell. Nothing you ate, did or were exposed to caused it, and nothing you do now can remove it.
Can I pass it to my children?
Each child has a one in two chance of inheriting it, sons and daughters alike. Testing usually waits until they are adults, because the risks it signals begin in adult life and screening does not start in childhood.
Does ATM affect ovarian cancer risk?
Any rise in ovarian risk appears small and the evidence is limited. Current guidance does not usually recommend removing the ovaries on an ATM result alone. A strong family history of ovarian cancer is weighed separately.
Does an ATM result change my cancer treatment?
Sometimes. In prostate and some other cancers, a fault in ATM or similar repair genes can open up certain targeted medicines. Your oncologist decides this, often using a tumour test as well as the blood test.
Should my partner be tested?
Usually only if you are planning children and the two of you are related by blood or from a small community. If both partners carry a fault, each child has a chance of ataxia-telangiectasia. Your counsellor can advise.
Where do I start after an ATM result?
Book a post-test counselling session and bring the full report and a list of cancers on both sides of the family. Call the CION helpline if you are not sure who to see, and we 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
Medical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Sources
- MedlinePlus Genetics — ATM gene
- GeneReviews (NCBI) — Ataxia-Telangiectasia
- National Cancer Institute — Genetics of Breast and Gynecologic Cancers (PDQ)
- NCCN — Genetic/Familial High-Risk Assessment: Breast, Ovarian, Pancreatic, and Prostate
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
ATM mutation: which cancers and what riskThe cancers an ATM fault is linked to, in plain termsATM positive: what happens nextThe first steps after a positive resultBiallelic ATM and ataxia-telangiectasiaWhen a child inherits two faulty copiesTesting the family for ATMWho in the family to test, and in what order
Talk to us
Holding an ATM report and not sure what it means?
Bring the report to a genetic counsellor who can explain it against your own family history. We can arrange that conversation, in Telugu if you prefer. One helpline serves every CION centre.