How Does a Mammogram Detect Breast Cancer?

What is a mammogram?

Mammography uses X-rays to create images of the breast. These images are called mammograms.

radiologist trained to read mammograms studies the images for signs of breast cancer.

In the past, mammogram images were stored on film (film mammography). Now, mammogram images are usually stored directly onto a computer (digital mammography).

Digital mammography images can be lightened or darkened, and certain sections can be enlarged and looked at more closely. Because the images are stored on a computer, they can be shared easily with another radiologist for review.

How is mammography used?


Breast cancer screening tools are used to find breast cancer in a person who doesn’t have any warning signs or symptoms.

Overall, mammography is the most effective screening tool used to find breast cancer in most women. It can find cancers at an early stage, when they are small and the chances of survival are highest.

Learn about mammography recommendations for women at average risk of breast cancer.

Learn about mammography recommendations for women at higher risk of breast cancer.


Mammography can also be used as a follow-up test when something abnormal is found on a screening mammogram or a clinical breast exam.

When used as follow-up test (instead of screening), a mammogram may be called a “diagnostic mammogram.”

Although it’s called a “diagnostic mammogram,” it can’t diagnose breast cancer. However, it can show whether the abnormal findings look like breast cancer. If the findings look like breast cancer, you will have a biopsy to diagnose (or rule out) breast cancer.

Whether you are getting a screening mammogram or a diagnostic mammogram, the basic procedure is the same. However, you will likely have more views with a diagnostic mammogram.

Getting a mammogram

If you are getting a mammogram for the first time, you may have questions about what to expect (before and after).

Learn about getting a mammogram, including information for women who have breast implants, are pregnant or breastfeeding or have a physical disability.

Findings on a mammogram

Like other X-ray images, mammograms appear in shades of black, gray and white, depending on the density of the tissue. Dense breast tissue and fatty breast tissue look different on a mammogram.

Learn more about breast density on a mammogram.

The results of a mammogram may show a benign (not cancer) condition or an abnormal finding that needs follow-up tests to rule out cancer.

Learn more about findings on a mammogram and when to expect your results.

Follow-up after an abnormal mammogram

For most women, a mammogram will show no signs of breast cancer.

However, if your mammogram does show something abnormal, you will need follow-up tests to check whether or not the finding is breast cancer.


Learn about follow-up after an abnormal mammogram.

Accuracy of mammograms

Although mammography is the most effective screening tool used today to find breast cancer in most women, it’s not perfect.

Learn about the accuracy of mammograms.

Weighing the risks and benefits of mammography

Most major health organizations have concluded that mammography saves lives.

However, there’s ongoing debate about how much benefit there is from mammography (especially in younger women) and whether this benefit outweighs the risks.

There’s also debate about when to begin mammography and how often to get a mammogram.

Learn more about the risks and benefits of mammography.

Radiation exposure during a mammogram

You’re exposed to a small amount of radiation during a mammogram.

While the radiation exposure during mammography can increase the risk of breast cancer over time, this increase in risk is very small [2-4].

Studies show the benefits of mammography outweigh the risks from radiation exposure, especially for women ages 50 and older [2-3,5]. 

Three-dimensional (3D) mammography (breast tomosynthesis)

What is 3D mammography?

Special imaging machines can take multiple two-dimensional (2D) digital images of the breast. Computer software combines the 2D X-ray images into a three-dimensional (3D) image (called breast tomosynthesis).

Radiologists must have special training to read these 3D images.

Getting a 3D mammogram

Getting a 3D mammogram is similar to getting a 2D mammogram.

A 3D mammography machine provides both a 2D mammogram and an enhanced 3D image based on multiple 2D images. All the images are taken on the same machine, so you stay in one place while all of the images are taken.

A 3D mammogram takes a few seconds longer than a 2D mammogram because more images are taken, but you won’t likely notice a difference (if you’ve had a mammogram in the past).

Depending on the method, 3D mammography gives the same or slightly higher radiation dose than standard 2D mammography. This higher dose is still within FDA guidelines [6-8].

Breast cancer screening

Some studies have shown 3D mammography may find a few more breast cancers than 2D mammography [6-10]. Whether 3D mammography is better than standard 2D mammography for breast cancer screening is still under study [6-10].

Currently, the American Cancer Society and the U.S. Preventive Services Task Force recommend standard 2D mammograms in their breast cancer screening guidelines [11-12].

The National Comprehensive Cancer Network breast cancer screening guidelines, however, note that 3D mammography may be considered [8].

Some centers offer 3D mammography. Although most insurance plans cover the cost, it’s best to check with your insurance provider and the imaging center before getting a 3D mammogram.

Learn more about screening recommendations for women at average risk

Low-cost or free mammograms

MedicareMedicaid and most insurance companies cover the cost of mammograms.

Since September 2010, the Affordable Care Act has required all new health insurance plans to cover yearly mammograms with no out-of-pocket costs (co-payments or co-insurance) for women ages 40 and older [84].

If you don’t have insurance or your insurance doesn’t cover mammograms, the organizations below can help you find a low-cost or free mammogram (or help with the cost).

  • Komen Affiliates fund breast cancer education and screening projects in their communities for those who need it most. Find your local Affiliate and learn about programs in your area.
  • Call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636) Monday through Friday from 9:00 a.m. to 10:00 p.m. ET and from 6:00 a.m. to 7:00 p.m. PT to find low-cost options in your area.
  • American Breast Cancer Foundation (ABCF) offers financial assistance for breast cancer screening and follow-up tests to uninsured women.
  • National Breast and Cervical Cancer Control Program provides access to breast cancer screening to low-income, uninsured and underinsured women.
  • Planned Parenthood offers clinical breast exams and referrals for mammography (and any follow-up testing, such as breast ultrasound).

Each October, during Breast Cancer Awareness Month, many imaging centers offer mammograms at reduced rates. To find a certified mammography center in your area, visit the FDA website (