A breast ultrasound isn’t a direct substitute for a mammogram, but it can be just as useful for people with concerns about breast cancer or who are at risk.

The two screening tests serve different yet similar purposes; you can say they complement each other. Both tests evaluate the breasts for signs of breast cancer or other conditions that alter your breast tissue.

Out of every 1,000 screening mammograms, a small number find breast cancer. In some situations, an ultrasound done after a mammogram (for example, to take a closer look at a specific area) or used as extra screening for certain higher-risk people can find cancers that are not evident in the mammogram.

Here, we explore eight important differences between mammograms and breast ultrasounds for breast cancer.

If you’re at an average risk for breast cancer, many guidelines recommend starting screening mammograms at age 40, but the schedule can differ — some recommend every year, while others recommend every other year. Your doctor can help you choose the timing that fits your risk and preferences.

Mammograms can detect breast cancer before it causes symptoms, and ideally, before it spreads. Mammograms are the main screening test proven to reduce the risk of dying from breast cancer.

Mammograms may also be used for making a breast cancer diagnosis if someone already has symptoms. Your doctor might recommend a diagnostic mammogram if you have breast cancer symptoms or if they detected something on a screening mammogram.

Ultrasounds, on the other hand, aren’t recommended for everyone. Your doctor might recommend a breast ultrasound to follow a mammogram if the mammogram was inconclusive, or if something was detected on the mammogram that needs a closer look.

A breast ultrasound can also be used to:

• Guide the needle for a breast biopsy
• Help screen for breast cancer in people at high risk
• Take a deeper look at dense breast tissue
• Assess a suspected breast infection or breast cyst
• Evaluate breast pain or a lump

Although both mammograms and breast ultrasounds can show images of the inside of your breast, they create these images in different ways.

Mammograms are a type of X-ray imaging test that passes low-dose radiation through your breast tissue to create a digital image.

A breast ultrasound isn’t an X-ray test. It uses high-frequency sound waves to create an image instead of radiation. The sound waves reflect off your breast tissue and back to the handheld transducer, which relays a live image onto a nearby screen.

Mammograms emit radiation, but it isn’t enough radiation to harm you. Mammograms use less radiation than conventional X-rays, which are used to take pictures of bones.

Any risk of harm from the radiation is generally outweighed by the benefits of getting screening mammograms for breast cancer. Mammograms can still be safe during pregnancy, but your doctor may recommend postponing mammograms until your pregnancy is over if you’re not high risk for breast cancer.

Breast ultrasounds emit no radiation whatsoever. In fact, there are no known risks to getting breast ultrasounds when they’re recommended.

Mastectomy is surgery to remove breast tissue to treat or help prevent breast cancer. After a mastectomy, many people don’t need routine screening imaging on the mastectomy side.

But if you notice a new lump, swelling, pain, skin changes, or another new concern in the chest wall or reconstructed breast, your doctor may use an ultrasound (or another imaging test) to take a closer look.

If you had a mastectomy on only one side, you’ll usually still need routine screening mammograms on the other breast.

A major way that the experience of getting a mammogram differs from getting a breast ultrasound is that mammograms involve compressing the breast. Compressing your breast prevents movement, which can cause a blurry image.

Breast compression during a mammogram also minimizes the amount of tissue that radiation needs to travel through. This allows mammograms to use lower radiation doses while also providing a clearer image.

Breast ultrasounds don’t require your breasts to be compressed. During a breast ultrasound, you lie still on an exam table. This can be a much more comfortable experience than getting a mammogram.

If you have dense breast tissue, your doctor may talk with you about whether you need any additional testing after a screening mammogram. In some cases, an ultrasound is one option, but it isn’t the right choice for everyone.

Having dense breast tissue means your breasts are made up of more glandular tissue than fat tissue. Dense breasts are a breast cancer risk factor, so your doctor may recommend more frequent breast cancer screenings if you have them.

Even though mammograms can’t see through dense breast tissue very well, the only way to find out if you have dense breasts is with a mammogram. Dense breasts are very common, and although they can increase your breast cancer risk, having them doesn’t mean that anything is wrong with your health.

Extra tests like ultrasound can sometimes find cancers that are harder to see on a mammogram, but they can also lead to more callbacks and biopsies that turn out not to be cancer.

Mammograms are great for initial breast cancer screenings because they can create a full picture of the breast using multiple images from different angles.

Some mammograms, called 3D mammograms (tomosynthesis), take pictures of different “slices” of your breast, then put them all together to produce a 3D digital image.

Breast ultrasounds don’t show the full breast all at once. Instead, they focus on one small, targeted area of the breast in question. This helps your healthcare provider see a concerning area of tissue closely and in more detail.

A breast ultrasound can work better than a mammogram for detecting and studying small tumors, which may not be visible on a mammogram. It also helps that tumors show up as a different color than regular breast tissue on a breast ultrasound, which isn’t the case with mammograms.

Neither mammograms nor breast ultrasounds are perfect in every way — each of them has limitations. These limitations can lead you to need further breast cancer tests or screenings in some cases.

Mammogram Limitations

Mammograms find the majority of breast cancers and breast tissue changes, but they’re not used alone to make a full breast cancer diagnosis. If your mammogram is abnormal, you’ll need further tests, such as an ultrasound or biopsy, next.

It’s also important to note that mammograms can miss cancers in some cases, often because those cancers are small or hidden within dense glandular tissue. Screening mammograms miss around 1 in 8 breast cancers, leading to false negative results.

False positive results can also happen with mammograms. This means you don’t have cancer, but a mammogram suggests that you may.

Breast Ultrasound Limitations

The main limitation of a breast ultrasound is that it can show only one small part of your breast at a time. That’s a big reason why ultrasounds can’t replace mammograms to screen for breast cancer.

In some cases, breast cancer isn’t visible on a breast ultrasound at all despite showing up on a mammogram. Fortunately, getting an ultrasound is risk-free. Additionally, some insurance plans don’t cover breast ultrasounds for breast cancer screening the way they cover mammograms.

Talk to Your Doctor

Talk to your doctor about how often to get breast cancer screenings based on your breast cancer risks. If you have a family history of breast cancer, a personal history of breast cancer, or know that you have dense breasts, you may need to get screening mammograms more often than most people.

Your doctor can also tell you if or when breast ultrasounds may be a necessary part of your care. Always report any breast changes right away, including breast lumps, nipple discharge, or skin changes.

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On MyBCTeam, people share their experiences with breast cancer, get advice, and find support from others who understand.

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