Are Mammograms Enough to Detect Breast Cancer?

Why does my doctor send me for a mammogram and a sonogram to screen for breast cancer? I am 43 and just had my fourth mammogram. Every time my gynecologist sends me for a mammogram, she sends me for a sonogram too. I am curious why she does this and if there is data to say that the extra testing is better?
—Squished x2

Over the years there has been controversy around when to start screening for breast cancer. The goal of screening is to find disease before it is symptomatic, when it can be treated more effectively. To do this, we want to use a test that is both sensitive and specific: that is, the test does a good job of finding the disease you are looking for and doesn’t find too much stuff that looks like the disease but isn’t.

The controversy around when to start breast cancer screening stems from the fact that younger women are more likely to have dense breast tissue. Dense breast tissue decreases the sensitivity — the likelihood of finding breast cancer when it is present — of mammography. Mammography misses up to 20% of breast cancers, and the more dense your breast tissue, the less sensitive mammography becomes.

When screening women with dense breast tissue for breast cancer with both a mammogram and a sonogram, you increase the sensitivity of screening but decrease the specificity. You find more stuff, including more breast cancer, but it is less likely that any individual finding is breast cancer.

There are several studies that look at mammography alone compared with mammography and breast sonogram in women with dense breasts. A 2023 Cochrane review found that adding breast sonography identifies two additional cases of breast cancer per 1,000 women screened — 0.45% of women screened were diagnosed with breast cancer in the mammogram plus sonogram group, compared with 0.3% in the mammogram-only group. However, a 2020 review found that in women with a normal mammogram, 90% of the findings on breast sonograms were false positives.

Ultimately, if you have dense breasts, which many women in their 40s do, having a breast sonogram in addition to your screening mammogram does increase the likelihood of finding breast cancer if you have it. But it also increases the likelihood of finding something that is not cancer and can lead to additional testing and mental distress. It is worthwhile to discuss both screening protocols with your doctor and decide whether a mammogram and sonogram or mammogram only is best for you.