I have dense breasts. Does that increase my risk of breast cancer?

DEAR DOCTOR K:

My doctor says I have dense breasts, and a friend says that means I have an increased risk of breast cancer. I’m hoping you’ll tell me that’s not so.

DEAR READER:

I wish I could fully reassure you, but I can’t. A woman who has dense breasts does have a slightly increased risk of breast cancer, although not clearly an increased risk of fatal breast cancer.

What are “dense” breasts? Women with dense breasts have relatively less fat in their breasts. Specifically, if more than 50 percent of your breasts are made up of other breast tissue (as opposed to fat), then by definition you are said to have dense breasts. It’s not uncommon; about 40 percent of women have dense breasts.

Dense breasts cause a second problem: They can make cancer harder to spot on standard mammograms. That’s because both breast tissue and tumors appear white on a mammogram. It’s easy to see individual snowflakes when they fall on a black glove, but it’s hard to see them when they rest on a bed of snow. That is the challenge radiologists face when trying to read the mammograms of a woman with dense breasts.

There now is a federal law in the United States that mammogram reports should always explicitly state whether a breast is dense or not.

So should you have additional screening tests for breast cancer? Probably yes, but don’t expect perfection. No test can diagnose breast cancer with 100 percent accuracy, especially in women with dense breasts. In addition, the additional tests that I’m about to describe pick up a lot of “false positive” test results.

False-positive results look like cancer, and therefore lead to a biopsy, but the biopsy shows no cancer. Until the result is known, a woman and her family understandably have anxiety. Also, the biopsy can lead to complications, like an infection, though that’s rare. Finally, the tests and the biopsy add financial costs.

Yet the additional testing may spot a cancer that might have been missed by a standard mammogram. The additional tests that are often done include:

  • ULTRASOUND. In September 2012, the FDA approved a new breast ultrasound system specifically for screening dense breasts. This ultrasound scans the entire breast using high-frequency sound waves and quickly produces several images. If you were going to have additional testing, your doctor most likely will recommend this ultrasound.
  • MAGNETIC RESONANCE IMAGING (MRI) uses magnets and radio waves to visualize the breasts. It is most valuable in women at higher risk for breast cancer that runs in families. However, it is not recommended specifically for dense breasts, and may have as many false-positive results as standard mammograms.
  • DIGITAL MAMMOGRAPHY sends X-ray images of the breast to a computer. It is somewhat more accurate than regular film mammography in women with dense breasts.

Talk with your doctor about the best way of detecting breast cancer because of your possible higher risk.

(This column is an update of one that ran originally in September 2013.)