Why NOT Annual Ultrasounds Instead of Annual Mammograms?

Screening Tests vs Diagnostic Tests for Breast Cancer

Radiologist reviewing results of patients mammogram
Why aren't annual breast ultrasounds used instead of mammograms?. Echo/Cultura/Getty

 If you've heard that mammograms can sometimes miss tumors, or that ultrasounds can play a role in diagnosis you may be wondering, "Why don't we have annual ultrasounds instead of mammograms?" After all, mammograms can be uncomfortable, expose you to radiation, and on top of that, breast ultrasounds are better at detecting some abnormalities.

Let's talk about the answer to this question, the differences between the two types of studies, Whether or not you have asked these questions the answer can help you to better understand the tests you may have in the future and the role for each.

Ultrasounds Are Diagnostic, Mammograms Are For Screening

The primary difference between mammograms and breast ultrasounds is the role they play.

Mammograms are a good screening test, meaning that they offer the most information for people who do not have any symptoms of breast problems. Screening ultrasounds, in contrast, would not be an effective breast cancer screening method for several reasons, including that they are unable to image the entire breast at once.

A breast ultrasound, in turn, is usually done for diagnostic reasons, frequently after a mammogram reveals a suspicious area or density in a breast. A breast ultrasound is good at distinguishing a benign fluid-filled cyst from a solid mass in the breast. With a cyst, an aspiration may be done under ultrasound to remove the fluid and eliminate the suspicious area entirely.

An ultrasound can also help define a mass in the breast that you feel yourself, even if it does not show up on a mammogram.

Limitations of Ultrasound

There are several limitations of breast ultrasound that would make it inappropriate for a screening test. These include:

  • Ultrasound cannot take an image of the whole breast at once as discussed above.
  • Ultrasound cannot take an image of areas deep inside the breast. Ultrasound is good for evaluating superficial lumps in the breast, but a mammogram is better able to note abnormalities that lie deeper in the breast.
  • Ultrasound cannot make 100 percent accurate diagnostic images.
  • Ultrasound doesn't show microcalcifications, the most common feature of tissue around a tumor. Many early breast cancers are first suspected based on calcifications in the breast. For a mass to be detected on ultrasound it usually must be significantly larger than what could be suspected from a mammogram.

Variables in the Accuracy of Both Mammograms and Ultrasounds

Neither technology, mammogram or ultrasound, is perfect. And in the case of ultrasound, the skill level of the operator makes a great difference in your results. One technician may miss something, while another technician may find it.

A breast ultrasound is very important even with a normal mammogram if you have a palpable lump. It's not uncommon for people who have found a lump (especially lumps near the surface of the breast) to have a normal mammogram. In this case, a breast ultrasound may detect a breast cancer better than a mammogram. The point here, however, is that when a lump is present we are not talking about screening, but rather diagnosis. In this setting, the breast ultrasound would be considered a diagnostic test to evaluate the lump.

Other Breast Imaging Technologies

Neither mammograms or breast ultrasounds find all breast cancers, and other options may be needed.

For example, for women at high risk of developing breast cancer, a breast MRI might be the best choice for screening. This is especially true for young women with dense breast for who mammography is not as accurate.

Other tests that may be recommended include elastography,  digital mammography, or optical mammography without compression. Breast thermography apparently works for some women. These techniques continue to evolve as researchers look for a better test to find breast cancers in the earliest stages of the disease possible.

Radiation Concern with Mammograms

The radiation exposure in a mammogram is very small.

It is about the same as is used in a dental x-ray and less than what is needed for a standard chest x-ray. Mammograms can painful for a brief period of time. The bottom line with pain, however, is that breast cancer surgery, which is usually more extensive with a larger tumor, is painful for a longer period of time.

The National Cancer Institute says the benefits of mammography outweigh the potential harm from the radiation exposure. However, be sure to alert your health care provider and the x-ray technician if there is any possibility you are pregnant, as they will want to avoid any radiation exposure to the fetus.

Bottom Line on Mammography vs Breast Ultrasound for Screening and Diagnosis

Mammograms are usually used as a screening test in people who do not have any breast symptoms. If a woman is having symptoms, such as a lump or nipple discharge, or if an abnormality is found on a mammogram, a breast ultrasound can be a very good diagnostic test to further evaluate the abnormality.

While breast ultrasounds are not good screening tests for breast cancer, there are options other than mammography for those who are at high risk or wish to avoid radiation (such as those who are pregnant.) In these settings a breast MRI might be a better, but much more expensive, screening test.

Sources:

Elmore, J. Screening for Breast Cancer: Strategies and Recommendations. UpToDate. Updated 06/05/17.

Macklin, S., Gass, J., Mitri, G., Atwal, P., and S. Hines. The Role of Screening MRI in the Era of Next Generation Sequencing and Moderate-Risk Genetic Mutations. Familial Cancer. 2017 June 22. (Epub ahead of print).

National Cancer Institute. Breast Cancer Screening (PDQ) – Health Professional Version. Updated 06/19/17. https://www.cancer.gov/types/breast/hp/breast-screening-pdq

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