Do mammograms save lives? Examining the claim — and the questions to ask

What the major trials and reviews show

Breast screening has been studied in large randomised trials since the 1960s, mostly in women aged around 40 to 74. Their results don't all agree, which is a big part of why the debate continues.

In the UK, an independent panel reviewed the trial evidence in 2012 and concluded that inviting women to screening reduced breast cancer deaths by about 20 per cent in those invited. They estimated that for every 10,000 UK women aged 50 invited to screening for 20 years, around 43 breast cancer deaths would be prevented and around 129 women would be diagnosed with a cancer that would never have caused them harm (Independent UK Panel on Breast Cancer Screening, 2012). Other analyses have reached higher estimates of benefit: long-term follow-up of the Swedish Two-County trial reported a reduction of around 30 per cent in breast cancer deaths among women invited (Tabár et al., 2011).

Others are more sceptical. A Cochrane review concluded that the most reliable trials showed a smaller benefit and substantial overdiagnosis (Gøtzsche & Jørgensen, 2013), and 25-year follow-up of the Canadian National Breast Screening Study found no reduction in breast cancer deaths (Miller et al., 2014). Both have been criticised in turn — the Canadian trial for aspects of its design, the Cochrane review for which trials it chose to weight. It is also worth knowing that most of these trials began decades ago, before many modern treatments, which may mean the benefit of screening today is different from what they measured.

The fairest reading is that screening probably reduces breast cancer deaths modestly, and that it also leads some women to be treated for cancers that would never have harmed them. Both are real.

Overdiagnosis and DCIS

Overdiagnosis means finding a genuine cancer, or pre-cancer, that would never have caused symptoms or death in a woman's lifetime. It isn't the same as a false alarm — the abnormality is real — but treatment can't benefit someone whose disease was never going to progress. The problem is that we can't yet reliably tell which ones those are.

Ductal carcinoma in situ (DCIS) sits at the centre of this debate. It is a change in the cells lining the milk ducts that hasn't spread into surrounding tissue, and screening finds a lot of it. A large study of women diagnosed with DCIS found that their risk of dying from breast cancer over 20 years was low — around 3 per cent — and similar to that of the general population (Narod et al., 2015). Trials such as LORIS in the UK are now testing whether careful monitoring could be a safe alternative to surgery for some low-risk DCIS (Francis et al., 2015). Results are still emerging, and DCIS isn't one condition — some types are higher risk than others.

Dense breasts

Breast density describes how much glandular and fibrous tissue there is compared with fat. Dense tissue appears white on a mammogram — and so do cancers, which makes them harder to spot. Higher density is also associated with a higher risk of breast cancer (Boyd et al., 2007).

This matters because many women don't know their density. Since 2024, US regulations have required that mammogram reports tell women about their breast density. In the Netherlands, the DENSE trial found that offering supplemental MRI to women with extremely dense breasts reduced the number of cancers diagnosed between screening rounds, though it is not yet known whether this reduces deaths (Bakker et al., 2019). If you have dense breasts, it is worth asking whether additional imaging is appropriate for you.

How much radiation a mammogram actually involves

A standard screening mammogram delivers a very low dose of radiation — roughly 0.4 millisieverts, which is often compared to around seven weeks of the natural background radiation we're all exposed to. Researchers who modelled the risk of radiation-induced breast cancer from regular screening estimated that it was small compared with the number of breast cancer deaths screening is expected to prevent (Yaffe & Mainprize, 2011).

Radiation risk is higher in younger women and in those with certain genetic variants, which is part of why screening schedules and imaging choices differ for women at high risk. For most women of screening age, though, radiation isn't the main reason to weigh up screening carefully — overdiagnosis is.

Where the alternatives stand

• Thermography: the US Food and Drug Administration has repeatedly warned that thermography is not a substitute for mammography and should not be used on its own for breast cancer screening. There is no good evidence it detects cancer early.
• Ultrasound: in a large Japanese trial, adding ultrasound to mammography in women in their 40s found more early cancers but also produced more false positives (Ohuchi et al., 2016). It is often used alongside mammography, particularly for dense breasts, but whether it reduces deaths is not known.
• 3D mammography (tomosynthesis): it can detect more cancers and reduce some recalls, but large trials are still assessing whether this translates into fewer deaths.
• MRI: established for women at high risk, such as those with BRCA variants, and increasingly studied for dense breasts. It is more sensitive but produces more false positives and is less widely available.
• Breast self-examination: a large trial in Shanghai found that teaching structured self-examination did not reduce breast cancer deaths (Thomas et al., 2002). Being breast aware — knowing what's normal for you and getting changes checked promptly — still matters.
• AI-supported reading: a Swedish trial found that AI-supported mammogram reading detected a similar number of cancers while reducing radiologist workload (Lång et al., 2023). It is promising, but long-term outcomes aren't known yet.

Questions to ask, not a verdict to obey

Screening recommendations differ: the NHS invites women aged 50 to 71 every three years, while US guidance recommends screening every two years from age 40 to 74 (US Preventive Services Task Force, 2024). In South Africa, access and recommendations vary, so it is best to discuss timing with your doctor. Wherever you are, these questions can help:

• What is my personal risk, considering my family history, genetics, breast density and hormonal history?
• Based on that, what are the likely benefits and harms of screening for someone like me?
• Do I have dense breasts, and would additional imaging be appropriate?
• If something is found, what are the next steps — and if it is DCIS, what are all the options, including monitoring where appropriate?
• How often should I be screened, and when should I review that decision?
• Should I be referred for genetic counselling or high-risk screening?

Screening is a personal decision, not a test of whether you are a 'good' patient. An informed choice either way deserves respect.

Risk you can influence

Whatever you decide about screening, some breast cancer risk factors are within reach. Alcohol is a well-established risk factor for breast cancer even at low intakes, which I've covered in my article on the alcohol health myth. Regular physical activity, maintaining a healthy weight after menopause and eating a diet rich in vegetables, fibre and whole foods are all sensible, although none of them guarantees protection. And if you notice a lump, skin change, nipple change or anything unusual, see your doctor promptly, whether or not you are due a screen.

Before you act on any of this

This article is for education and general information only. It isn't medical advice, it can't diagnose or treat any condition, and it doesn't replace a consultation with your own doctor or a qualified practitioner who knows your history. Please don't start, stop or change any medication, hormone or supplement because of something you've read here — take your questions to the person responsible for your care.

If you have symptoms, a strong family history or a known genetic variant, please speak to your GP or a breast specialist rather than relying on routine screening schedules.

References

• Bakker, M.F., de Lange, S.V., Pijnappel, R.M., et al. (2019). Supplemental MRI screening for women with extremely dense breast tissue. New England Journal of Medicine, 381(22), 2091–2102.
• Boyd, N.F., Guo, H., Martin, L.J., et al. (2007). Mammographic density and the risk and detection of breast cancer. New England Journal of Medicine, 356(3), 227–236.
• Francis, A., Thomas, J., Fallowfield, L., et al. (2015). Addressing overtreatment of screen detected DCIS; the LORIS trial. European Journal of Cancer, 51(16), 2296–2303.
• Gøtzsche, P.C., & Jørgensen, K.J. (2013). Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews, (6), CD001877.
• Independent UK Panel on Breast Cancer Screening. (2012). The benefits and harms of breast cancer screening: an independent review. The Lancet, 380(9855), 1778–1786.
• Lång, K., Josefsson, V., Larsson, A.M., et al. (2023). Artificial intelligence-supported screen reading versus standard double reading in the Mammography Screening with Artificial Intelligence trial (MASAI). The Lancet Oncology, 24(8), 936–944.
• Miller, A.B., Wall, C., Baines, C.J., et al. (2014). Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ, 348, g366.
• Narod, S.A., Iqbal, J., Giannakeas, V., Sopik, V., & Sun, P. (2015). Breast cancer mortality after a diagnosis of ductal carcinoma in situ. JAMA Oncology, 1(7), 888–896.
• Ohuchi, N., Suzuki, A., Sobue, T., et al. (2016). Sensitivity and specificity of mammography and adjunctive ultrasonography to screen for breast cancer in the Japan Strategic Anti-cancer Randomized Trial (J-START). The Lancet, 387(10016), 341–348.
• Tabár, L., Vitak, B., Chen, T.H.H., et al. (2011). Swedish Two-County Trial: impact of mammographic screening on breast cancer mortality during 3 decades. Radiology, 260(3), 658–663.
• Thomas, D.B., Gao, D.L., Ray, R.M., et al. (2002). Randomized trial of breast self-examination in Shanghai: final results. Journal of the National Cancer Institute, 94(19), 1445–1457.
• US Preventive Services Task Force. (2024). Screening for breast cancer: US Preventive Services Task Force recommendation statement. JAMA, 331(22), 1918–1930.
• Yaffe, M.J., & Mainprize, J.G. (2011). Risk of radiation-induced breast cancer from mammographic screening. Radiology, 258(1), 98–105.