The ATM gene builds a protein that works like a smoke alarm for DNA, telling a cell when its genetic material is damaged and needs repair. Inheriting one faulty copy leaves that alarm weaker, so a few damaged cells can slip through toward cancer. The rise in risk is moderate: roughly two to three times the average for breast cancer in women, with smaller added risks for pancreatic and prostate cancer. It is far from the near-certain risk people associate with BRCA genes, and most carriers never develop cancer. Your exact variant and the rest of your genes also shape the odds, so two carriers can face quite different risks.
What the ATM Gene Does in Your Cells
The ATM protein is a first responder to the worst kind of DNA damage. It switches on quickly when both strands of the DNA ladder snap, the most dangerous kind of break.1PubMed. Activation and regulation of ATM kinase activity in response to DNA double-strand breaks From there it sits at the top of the cell’s damage response and sets off a large network of repair and safety steps.2PubMed. The ATM protein kinase: regulating the cellular response to genotoxic stress, and more It also responds to damage from oxidative stress, a normal by-product of using oxygen.3PubMed Central. ATM’s Role in the Repair of DNA Double-Strand Breaks
When ATM senses a double-strand break, it signals the cell to pause its division cycle, so repair has time to happen before the damaged DNA is copied. If the damage is too severe to fix, a working alarm can push the cell to self-destruct, removing it before it can become a cancer cell. With only one working copy, this pause-or-destroy response is weaker rather than absent, so most damage is still handled and only some cells slip through.
Without ATM, repairs go wrong. The protein is needed both to start and to finish the most accurate form of DNA repair.4PubMed Central. Involvement of ATM in homologous recombination after end resection and RAD51 nucleofilament formation When it is missing, cells fall back on a sloppier repair that can fuse chromosomes together.5PubMed Central. ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks
Everyone has two copies of ATM. A harmful mutation in one copy makes you a carrier; your lab report may call it a pathogenic variant. About 0.35% of people, around 1 in 300, carry one.6Fox Chase Cancer Center. Gene Linked to Breast Cancer Also Raises Risk for Other Cancers, Study Shows People with two faulty copies have ataxia-telangiectasia (A-T), a rare disease of nerve damage, weak immunity, and cancer at young ages.7PubMed. Ataxia-Telangiectasia, DNA Repair Deficits, Immune Dysfunction, and Cancer: A Review of Mechanisms, Clinical Presentations, and Emerging Therapies Carriers keep one working copy, which is why their added risk is moderate rather than extreme.
Carriers don’t get A-T symptoms such as balance problems, because one copy makes enough protein for daily life. The weakness shows only under repeated DNA damage over decades.
Even the one good copy can fail. Cancer often starts when a cell loses it by chance. Pancreatic tumours in carrier families showed exactly this loss of the good copy. Because that loss happens only by chance, risk is raised but not certain.
Breast Cancer Risk for ATM Carriers
When studies are pooled, women carrying an ATM mutation have about three times the average breast cancer risk.8PubMed. Health risks for ataxia-telangiectasia mutated heterozygotes: a systematic review, meta-analysis and evidence-based guideline Another large analysis puts it at about twice the average overall.9PubMed. Cancer risks and mortality in heterozygous ATM mutation carriers Before age 50, though, the risk was about five times the average,10PubMed. Cancer risks and mortality in heterozygous ATM mutation carriers so the added risk is concentrated at younger ages. Estimates vary; one population study put lifetime risk by 80 at about 13%, with wide uncertainty.11PubMed Central. Population-based estimates of age-specific cumulative risk of breast cancer for pathogenic variants in ATM
The numbers differ partly because of who was studied. Some studies recruit families with many cancers, which inflates estimates. Population studies include carriers with no family history at all. Your own family history pushes you toward one end of the range or the other.
For context, an average woman has about a 1 in 8 lifetime risk of breast cancer. For many carriers, lifetime risk lands somewhere around 20 to 30%. That places ATM as a moderate-risk gene, below BRCA1 and BRCA2.12Clinical Cancer Research. Reclassification of ATM Missense Variants of Uncertain Significance by Integrating Results from Systematic Functional Assays into an ACMG Points–Based Framework
A “twice the risk” figure is not a prediction: doubling a 1 in 8 risk still leaves most carriers cancer-free. A genetic counsellor can give you your own lifetime percentage.
Age matters too. The jump in risk before 50 means the years around 40 count most for carriers, which is why screening starts earlier than for the general population. Risk does not switch off after 50, so carriers should keep screening and not stop early.
Pancreatic, Prostate and Other Cancers
Inherited ATM mutations raise the risk of pancreatic cancer.13PubMed Central. ATM mutations in hereditary pancreatic cancer patients About 2 to 3% of people from families with several pancreatic cancers carry one ATM mutation.14Lustgarten Foundation. About Familial Pancreatic Cancer ATM mutations appear in 1 to 5% of all pancreatic cancer patients.15Lustgarten Foundation. About Familial Pancreatic Cancer Most carriers will not get pancreatic cancer.
Pancreatic cancer weighs differently than breast cancer. It is often found late because early symptoms are vague, which is why even a modest added risk gets doctors’ attention. Family history is the clue that matters most: a carrier with several affected relatives is in a different position from one with none. A carrier with no pancreatic cancer in the family is usually not offered pancreatic screening, since the benefit is less clear.
Men with prostate cancer were about four times more likely than men without it to carry a harmful ATM variant.16PubMed Central. Rare Germline Variants in ATM Predispose to Prostate Cancer: A PRACTICAL Consortium Study The link was stronger in men diagnosed before 65.17PubMed Central. Rare Germline Variants in ATM Predispose to Prostate Cancer: A PRACTICAL Consortium Study In one study, more than half of men with ATM, BRCA2 or NBN mutations had high-grade, fast-growing tumours, versus about 1 in 5 without.18PubMed. Mutations in ATM, NBN and BRCA2 predispose to aggressive prostate cancer in Poland
That matters because many prostate cancers grow slowly and need only watching. An ATM result can tip doctors toward earlier screening and treatment. And since male relatives of female carriers can inherit ATM too, the result can matter for men who never expected it to.
Carriers also have more digestive tract cancers.19PubMed. Health risks for ataxia-telangiectasia mutated heterozygotes: a systematic review, meta-analysis and evidence-based guideline They have somewhat shorter life expectancy, from cancer and heart disease, with about 1.7 times the risk of dying from these.20PubMed. Health risks for ataxia-telangiectasia mutated heterozygotes: a systematic review, meta-analysis and evidence-based guideline
Screening If You Carry an ATM Mutation
- Warning signs: all carriers should be taught the warning signs of ATM-related cancers: new breast lumps or skin changes; unexplained weight loss, new diabetes or jaundice, which can point to the pancreas; and urinary changes in men.21Facing Our Risk of Cancer Empowered. ATM Gene Mutation: Screening Guidelines
- Women: a yearly mammogram and usually a breast MRI, starting around age 40.
- Men: a yearly PSA blood test may be considered from age 40.22Journal of the National Comprehensive Cancer Network. NCCN Guidelines Insights: Genetic/Familial High-Risk Assessment: Breast, Ovarian, Pancreatic, and Prostate, Version 2.2026
- Pancreas: screening may be considered from age 50, or 10 years before the youngest pancreatic cancer in the family, whichever is earlier.23Journal of the National Comprehensive Cancer Network. NCCN Guidelines Insights: Genetic/Familial High-Risk Assessment: Breast, Ovarian, Pancreatic, and Prostate, Version 2.2026
MRI is added to mammograms because it can detect some cancers a mammogram misses, which matters since breast tissue in younger women is often dense. The two are often done at different times of year so a check happens every six months or so, though schedules vary by clinic.
A PSA is a protein made by the prostate, and a rising level can signal a problem that needs further tests. A raised PSA does not mean cancer, since benign prostate enlargement and infection can also raise it. Men are usually advised to discuss the pros and cons first, because screening can find slow-growing cancers that would never have caused harm.
Pancreatic screening is usually advised mainly when a close relative has had pancreatic cancer. It typically means an MRI or an endoscopic ultrasound, where a small scope passes through the stomach to look at the pancreas. It is done at specialist centres and aims to catch tumours before symptoms appear.
Bring a written family cancer history, with ages, to your appointment. Risk-reducing mastectomy is not routinely advised for ATM alone, unlike BRCA.
Radiation and Cancer Treatment for Carriers
People with A-T are extremely sensitive to radiation.24PubMed. Ataxia-Telangiectasia, DNA Repair Deficits, Immune Dysfunction, and Cancer: A Review of Mechanisms, Clinical Presentations, and Emerging Therapies In carriers the effect varies widely from person to person.25PubMed Central. Increased radiation toxicity with germline ATM variant of uncertain clinical significance In one group of breast cancer patients, all three who had severe late skin and tissue damage after radiotherapy carried ATM mutations.26PubMed. ATM mutations in female breast cancer patients predict for an increase in radiation-induced late effects Tell your radiation oncologist about your ATM result before treatment.
Most carriers tolerate radiotherapy without unusual problems, so a result is not a reason to avoid it when it is needed. The reactions in that small group were to normal tissue such as skin, appearing months or years after treatment. No test reliably predicts who will react strongly, so the practical step is for the team to know your status and watch for side effects. Routine mammogram doses are tiny compared with radiotherapy, and guidelines still recommend mammograms for carriers.
On the treatment side, cells lacking ATM are far more sensitive to PARP inhibitors, cancer drugs that block another repair route, in lab tests.27PubMed Central. PARP inhibitor synthetic lethality in ATM biallelic mutant cancer cell lines is associated with BRCA1/2 and RAD51 downregulation Lab-grown cells with no working ATM were 45 to 80 times more sensitive to one such drug.28Cancer Research. Abstract 2379: Elaborating the mechanism of PARP synthetic lethality in ATM loss But these are lab results, and carrier tumours that keep a working copy respond less.29PubMed Central. PARP inhibitor synthetic lethality in ATM biallelic mutant cancer cell lines is associated with BRCA1/2 and RAD51 downregulation
If you are being treated for cancer, useful questions for your team are whether your tumour was tested for ATM loss, whether a PARP inhibitor or clinical trial fits, and whether radiation doses or methods should change.
Why Your Personal Risk May Differ
Risk depends on the exact variant, and one variant, c.7271T>G, carries higher breast cancer risk than others.30GeNotes. ATM-associated cancer risk Carriers of c.7271T>G had nearly four times the breast cancer odds, versus about two times for other harmful variants.31Cancer Prevention Research. Germline Pathogenic Variants in the Ataxia Telangiectasia Mutated (ATM) Gene are Associated with High and Moderate Risks for Multiple Cancers Variants differ in how much they disrupt the ATM protein, so some leave a partly working protein and others leave almost none. The c.7271T>G change is different because the faulty protein it makes can interfere with the working copy. That is why a report naming your exact variant is more useful than the word “ATM” alone.
Thousands of ATM changes are labelled variants of uncertain significance (VUS), meaning no one yet knows if they are harmful.32Clinical Cancer Research. Reclassification of ATM Missense Variants of Uncertain Significance by Integrating Results from Systematic Functional Assays into an ACMG Points–Based Framework That means science has not gathered enough evidence to call the change harmful or harmless, not that it is probably harmful. A VUS should not change your screening by itself. Your care usually follows your personal and family history, as it would for someone without a result, and family members are generally not tested for a VUS because their result could not be interpreted either.
On your report, “pathogenic” or “likely pathogenic” means the screening advice applies. An uncertain result can be reclassified later, so ask the lab to notify you of updates.
Your other genes matter as well. A polygenic risk score adds up hundreds of tiny gene differences to estimate breast risk.33JAMA Network Open. Association of a Polygenic Risk Score With Breast Cancer Among Women Carriers of High- and Moderate-Risk Breast Cancer Genes ATM carriers with the lowest scores may have breast risk near the population average.34JAMA Network Open. Association of a Polygenic Risk Score With Breast Cancer Among Women Carriers of High- and Moderate-Risk Breast Cancer Genes In one analysis, about half of ATM carriers with no affected mother or sister had a lifetime risk above 20%, versus nearly 8 in 10 with one.35PubMed Central. Risk of Breast Cancer Among Carriers of Pathogenic Variants in Breast Cancer Predisposition Genes Varies by Polygenic Risk Score Combining scores and family history, about 1 in 3 carriers had low risk and 1 in 10 high.36PubMed Central. Comprehensive Breast Cancer Risk Assessment for CHEK2 and ATM Pathogenic Variant Carriers Incorporating a Polygenic Risk Score and the Tyrer-Cuzick Model
Lifestyle evidence is thin. Diet links are weak and come from small studies of common gene differences. Normal advice still applies: don’t smoke, limit alcohol, stay active. No supplement is proven to offset ATM.
What an ATM Result Means for Your Family
Each child, sibling and parent of a carrier has a 1 in 2 chance of carrying it. Share your result so relatives can decide about testing. Each relative’s chance is independent, so one sibling testing positive says nothing about another. Testing matters most for blood relatives on the side of the family the mutation came from. A relative who tests negative for the specific variant found in your family can usually be treated as not carrying it.
Men can carry and pass on ATM just as women can. Children usually aren’t tested until adulthood, since screening starts around 40.
If both parents carry ATM mutations, each child has a 1 in 4 chance of A-T. A partner can be tested before pregnancy. With one carrier parent, A-T is not a concern because it requires two faulty copies. Children may be carriers but won’t have A-T, and their own cancer screening decisions come as adults.
When both parents are carriers, IVF with embryo testing can select embryos without the mutation.37Facing Our Risk of Cancer Empowered. Ataxia-Telangiectasia and Other Medical Concerns Associated with ATM Mutations In the UK it is approved when both parents carry ATM, or one has c.7271T>G.38GeNotes. ATM-associated cancer risk Other choices include prenatal testing, donor eggs or sperm, adoption, or testing children as adults.39GeNotes. ATM-associated cancer risk Carriers seeking fertility treatment are offered genetic counselling about these options.40Fertility and Sterility. Clinical outcomes of patients who are carriers of Ataxia-Telangiectasia (ATM) variants seeking fertility treatments