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Breast density – facts, not fear

Only in America can we find a way to scare the bejesus out of a woman with normal breasts and a normal mammogram. But that's exactly what breast density notification laws, currently in effect in about half the states in America, are doing.

I know, because I get the worried phone calls from patients who, along with their normal mammogram results, have received a letter telling them:  "Your mammogram shows that your breast tissue is dense. Dense breast tissue is very common and is not abnormal … but can make it harder to find cancer on a mammogram and may also be associated with an increased risk of breast cancer. Talk to your doctor about your own risks for breast cancer."

The information mandated by the law is just enough to scare any women who happens to have dense breasts, but not enough to help her understand what this really means.

If you've gotten a letter telling you your breasts are dense, don't be afraid. Having dense breasts is entirely normal, especially if you are under age 60.  Here's what you need to know.

Breast Density is a Technical Term, not an Abnormal Diagnosis 

Breast density is a radiologic term that describes how well x-rays pass through the breast tissue. It is a surrogate for how much of the breast is fatty and how much is glandular. The radiologist reading the mammogram classifies the breast composition as one of the following:

  1. Almost entirely fat (<25% glandular)

  2. Scattered fibroglandular densities (25-50%)

  3. Heterogeneously dense breast tissue (51-75% glandular)

  4. Extremely dense (> 75% glandular)

For the purposes of breast density laws, any woman whose breasts are heterogeneously or extremely dense are notified that they have dense breasts.

Breast density is subjective

Different radiologists may assign the same mammogram different density ratings. Computerized density measurement could decrease this variability, but there is not yet a standardized computer density rating system.

Breast density can vary across a woman's menstrual cycle and over her lifetime.  

That means that the same woman, scanned at a different time in her cycle or at a later year, may or may not be told she has dense breasts.

Dense breasts are extremely common, especially in younger women. 

According to a recent report of mammograms in New York City, 74% of women in their 40s, 57% of women in their 50′s, 44% of women in their 60′s and 36% of women in their 70′s have dense breasts.

Increased breast density may be a risk factor for getting breast cancer. 

The mechanism is unknown, but it could be that breast density is just the end result of other factors that increase breast cell proliferation and activity – factors like genetics and postmenopausal hormone use.

How much of a risk? Well, it depends. In older women, those with extremely dense breasts have a three to five-fold higher cancer risk than those with mostly fatty breasts. The risk is lower than that in women in the middle category of breast density and in younger women, though not well-defined.

The truth is, we really have no way to translate individual breast density into individual breast cancer risk. But the biggest problem with considering breast density as a risk factor for breast cancer is that most women at some point in their lives have dense breasts. Should we really consider 75% of women in their forties to be at increased risk for breast cancer?

Dense breasts can obscure a cancer on mammogram.

Overall, about 10% of breast cancers are missed by mammograms. That percentage may be higher if a woman has dense breasts. The exact miss rate depends on her risk to start with, which depends on age and other risk factors.

Digital mammograms may be better at finding breast cancers in women with dense breasts who are near menopause or under age 50, but it is not known yet if this translates into less breast cancer deaths.

We do not know if additional breast cancer ultrasound saves lives.

Breast ultrasound and/or MRI for breast cancer screening is currently not recommended based on breast density alone. Adding this screening may pick up more cancers, but it does not save lives.

Additional screening beyond mammography is only recommended for women at highest risk for breast cancer. That includes those with a high risk gene mutation, a family history suggesting one of these mutations, or a history of chest irradiation prior to age 35. Even in this group, declines in mortality with the additional screening have not yet been shown, and the rate of false alarms with this additional testing is extremely high.

Additional screening beyond mammograms adds significant costs to breast cancer screening.

For some women, this additional cost may not be covered by insurance.  Not all states that mandate breast density notification also mandate insurance coverage for additional screening.

What should you do if you've been told your breasts are dense on mammography? 

If you are at increased risk for breast cancer due to personal or family history, you may want to consider adding ultrasound or MRI screening. (Tools for assessing your risks for breast cancer include the BCSC Risk calculator and the NCI breast cancer risk calculator.)

If you are not at increased risk for breast cancer and have dense breasts, there is no recommendation that you do anything other than continue screening at whatever interval you and your doctor have decided is right for you. If you decide you nonetheless want an ultrasound, understand that you will need to accept the additional false positives and biopsies that may result and that the additional screening has not been shown to decrease deaths from breast cancer in women at average risk.

More info on mammograms and breast density

  1. Breast Density info from Breast Screening Decisions

  2. Mammogram Fact Sheet from National Cancer Institute

  3. Breast Density Fact Sheet from the American Cancer Society

  4. Breast Density Info from Memorial Sloan Kettering doc Carol Lee

  5. – a great site for docs and patients alike

Margaret Polaneczky is an obstetrician-gynecologist at Weill Cornell Medical College and New York Presbyterian Hospital in New York City. She is a Philadelphia-area native, proud graduate of Villanova University and the Temple University School of Medicine, and former faculty member at the University of Pennsylvania School of Medicine. Read more at her blog, The Blog that Ate Manhattan.

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