Can Radiation From Mammograms Cause Breast Cancer?

This page is for anyone worried that the x-rays from mammograms could cause breast cancer. It compares the dose with everyday radiation and explains what studies estimate about the balance of risk and benefit.

The claim is that mammogram x-rays cause more breast cancer than screening prevents, so regular mammograms do more harm than good. It usually opens with something true: ionizing radiation can cause cancer. Then it stops there, without putting a number on either side.

A screening mammogram delivers roughly 0.3 to 0.4 millisieverts (mSv) of radiation. Published figures vary a little with breast size and equipment. A 3D mammogram, also called tomosynthesis, is somewhat higher.

For comparison, the average person in the United States takes in about 3 mSv a year from natural background radiation alone. That comes from cosmic rays, radon, and naturally radioactive elements in soil, food, and your own body. So one mammogram is roughly five to seven weeks of ordinary background exposure. A chest x-ray is about 0.1 mSv. A CT of the abdomen and pelvis is about 7.7 mSv, more than twenty-five times a mammogram.

The risk is not zero. Researchers have tried to size it rather than wave it away.

A modeling study was published in Annals of Internal Medicine in 2016. Its funders included the National Cancer Institute and the U.S. Preventive Services Task Force. It looked at annual digital mammography screening of 100,000 women aged 40 to 74. The model projected about 125 breast cancers caused by the radiation, leading to about 16 deaths. In the same group, screening was projected to prevent 968 breast cancer deaths. That is roughly sixty deaths prevented for every one caused.

The same study found the balance shifts with how you screen. Switching from annual screening starting at 40 to screening every two years starting at 50 cut the projected radiation risk about fivefold. Women with large breasts often need extra views for a complete exam. For them, the projected risk was higher: about 266 radiation-induced cancers and 35 deaths per 100,000, against 113 and 15 for everyone else.

It does not mean the radiation is imaginary. And it does not mean more imaging is always better.

The numbers above are projections from models, not counts of real people. The American Cancer Society says it is hard to study cancer risk from imaging tests because they use lower doses than most other exposures, such as the exposure of atomic bomb survivors. So the estimates rest on models.

It also does not mean radiation is the main downside of screening. USPSTF says the most common harm of screening mammography is a false-positive result. That means being called back for extra imaging or a biopsy for something that turns out not to be cancer. It can lead to extra testing and worry.

Finally, none of this settles when you personally should start, or how often to go. The USPSTF recommends screening mammography every other year for women aged 40 to 74. Family history, genetic risk, breast density, and how much a false alarm bothers you all matter. That weighing belongs with your care team, not a formula.

Mammograms use real radiation. The dose is about five to seven weeks of the background radiation you live in anyway. The best current estimates say screening prevents far more breast cancer deaths than its radiation could plausibly cause. Is radiation on your mind? Bring it up directly. Ask what schedule your clinician recommends for someone with your history, and why.

• Miglioretti et al., Radiation-Induced Breast Cancer Incidence and Mortality From Digital Mammography Screening (Ann Intern Med, 2016)
• USPSTF: Breast Cancer Screening recommendation (2024)
• American Cancer Society: Understanding Radiation Risk from Imaging Tests
• RadiologyInfo.org: Radiation Dose from X-Ray and CT Exams