More on Breast Density Notification Laws

There’s a nice discussion of the practical considerations around breast density notification laws in this week’s NEJM.

The editorial and accompanying podcast summarize what we do and don’t know about breast density, and give practical suggestions for incorporating breast density into the discussion around mammography screening for individual patients.  Online access to both the editorial and podcast discussion is free, and I encourage you to read and listen.

Bottom line  

Most women under age 60 will have dense breasts on mammography. Breast density is subjective, and we do not as yet have a computerized way of standardizing breast density readings. Breast density can also vary in a given women across the menstrual cycle and with age.

Breast density may increase breast cancer risk from 1.2-2 times, but it is not clear if that increased risk is additive to other factors that already increase breast cancer risk – family history, lifestyle, reproductive history – or just a manifestation of that risk.  No current breast cancer risk model incorporates breast density.

At this point in time, mammography is the only breast cancer screening that has been shown to reduce breast cancer mortality. There is little evidence to support routine supplemental screening sonograms in women at average risk of breast cancer who have dense breasts.

In women at average risk for breast cancer with dense breasts, screening breast sonograms will detect less than 1 additional cancer per 1,000 women screened. In this group of women, supplemental sonography has not been shown to decrease breast cancer mortality and carries high rates of false positives. (Only 6% of biopsies will show cancer.)

In women at higher than average risk for breast cancer, sonograms in those with dense breasts pick up an additional 3.2 cancers per 1000 women screened.  How this may translate into reduce breast cancer mortality is not known. Women with a lifetime risk of breast cancer >20% are advised to consider breast MRI , which identifies an additional 8.5 cancers per 1000 women screened and has been shown to be cost effective in this population.

My take

Breast density notification laws, while well-intentioned, unnecessarily alarm women with normal mammograms by telling them they “may be at increased risk of breast cancer”.

A better approach would be to simply notify women that breast density may obscure masses that mammograms miss but sonograms may detect, albeit with higher rates of unnecessary biopsies and no proven efficacy in reducing breast cancer mortality in women at average risk for breast cancer.  Then let women make an informed choice about sonograms based on this information and their own risks.

One of the arguments made for screening sonograms  is that they allow for earlier diagnosis of masses that evade mammography, leading to less need for advanced treatments such as chemotherapy. Given that chemotherapy is now being targeted to tumor type and not just stage, this advantage of earlier stage diagnosis may not prove as large as some would hope.

The best approach to breast cancer screening at this time is to target it based on risk.

You can learn your breast cancer risk here.  Talk with your doctor about the benefits and harms of mammography, when to start screening, and how often to be screened. If your breasts are dense, and you are at increased risk for breast cancer, you  may consider additional screening with sonogram, although its benefits are not known. If your lifetime breast cancer risk is >20%, consider supplementing mammograms with breast MRI.

Age is one of the strongest risk factors for breast cancer, and it’s why mammograms are recommended every 1-2 years starting at 50 in all women, regardless of other risk factors.  Some groups, including the American College of Obstetricians & Gynecologists, recommend annual mammograms starting at age 40 for all women.  Others, including the US Preventive Services Task Force, recommend individualized screening schedules for women ages 40-49 based on risk and personal preference.   We’ve developed an online decision aid for women ages 40-49 that can help you and your doctor come to a screening decision that’s right for you.

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More info on mammograms and breast density

• Dense Breasts on Mammogram? No Need to be Afraid.
• Mammogram Fact Sheet from National Cancer Institute
• Breast Density Fact Sheet from the American Cancer Society
• Breast Density Info from Memorial Sloan Kettering doc Carol Lee
• www.BreastDensityInfo – a great site for docs and patients alike