Can radiation from mammograms cause cancer?

What do you think is more likely to cause breast cancer: chemicals such as BPA, phthalates, and pesticides or imaging tests such as X-rays and CT scans? The surprising answer: the imaging tests, particularly CT scans but also X-rays and even the mammograms used to detect breast cancer.

The Institute of Medicine, the nonprofit health arm of the National Academy of Sciences, reviewed possible causes of breast cancer in 2012 and found that no product or chemical could be conclusively linked to the malignancy. Not so for radiation-based imaging tests. The report, "Breast Cancer and the Environment: A Life Course Approach," concluded that about 2,800 breast-cancer cases a year among U.S. women stem from medical radiation.

"While these represent a small proportion of all breast cancers, they're important because they can potentially be reduced," said Rebecca Smith-Bindman, M.D., director of the Radiology Outcomes Research Laboratory at the University of California at San Francisco, in an analysis of the findings.

The IOM concluded that one of the most important steps women can take to reduce their breast-cancer risk is to avoid unnecessary imaging tests. (Find out when to question CT scans and X-rays.)  

Learn more about the dangers of CT scans and X-rays and check our advice on screening tests for breast cancer and other malignancies.

But that advice becomes tricky when it comes to mammograms. After all, mammograms are proven to reduce your risk of dying of breast cancer, by helping to detect the malignancy early, when it's more easily treated. So how do you balance that against the slight breast cancer risk posed by mammograms? Here's our advice.

Should you still get mammograms?

Yes—but not more often than necessary. Mammograms don't expose you to much more radiation than a traditional chest X-ray, and the risk posed by a single scan is extremely small. Still, any needless exposure poses needless risk. And some doctors recommend that women get screened every year, or start at a young age. We think that's usually not necessary. The U.S. Preventive Services Task Force, whose advice helps set government policy on screening tests, says women ages 50 to 74 should get screened every two years. Those in their 40s or 75 and older should talk with a doctor to see whether the benefits outweigh the potential harm.

Can ultrasound or MRI of the breast be used instead?

Neither of those tests emit radiation, but they are usually paired with regular mammograms, not offered as an alternative. So they can't really help you avoid radiation from mammography. And while adding them to regular mammography may improve cancer detection, the combination tests are more likely to trigger false alarms. Moreover, there's no convincing evidence that adding the tests to mammography saves more lives. The tests may make most sense for women with "extremely dense" breasts—that is, who have relatively little fat in their breast tissue—since they face a greater breast cancer risk, in part because mammography is less accurate in them.

What about 3D mammography?

You may be hearing more about this form of mammography, which goes by the technical name tomosynthesis. It exposes you to about as much radiation as a regular mammogram, but allows radiologists to view the breast in detailed slices instead of a single, flat image. With more views of the breast, the radiologist can zoom in on areas-in-question and better determine whether more testing is needed.

Piggybacking tomosynthesis and mammography can increase cancer detection rates while cutting the number of invasive follow-up tests in those with questionable mammograms. But it's not yet proved to save additional lives.

But because the test is done in combination with a standard mammogram, until recently it meant getting a double dose of radiation. That's now changed. The Food and Drug Administration recently approved a tomosynthesis scanner that creates both 2D (standard mammography) and 3D images at the same time, eliminating the increase in radiation exposure. So if your doctor suggests a 3D mammogram, make sure it's with the newest version of the technology.

—David Schipper