Dense Breasts Are Just One Part Of The Cancer Risk Calculus

Almost half the states now require doctors to tell women if they have dense breasts because they're at higher risk of breast cancer, and those cancers are harder to find. But not all women with dense breasts have the same risks, a study says.

Those differences need to be taken into account when figuring out each woman's risk of breast cancer, the study says, and also weighed against other factors, including family history, age and ethnicity.

The researchers looked at the records of 365,426 women who had a normal mammogram, then looked to see which ones were diagnosed with breast cancer within a year — a cancer that may have been missed by the mammogram.

All told, 47 percent of the women in the study had dense breasts. But just half of those women had a higher cancer risk. The women who got cancer were more likely to be older and white, have a family history of breast cancer, and to have "heterogeneously" or "extremely" dense breasts, the top two categories of breast density.

The results were published Monday in Annals of Internal Medicine.

Breast cancer advocates have been pushing for state and federal laws requiring that women be told if they have dense breasts, so they can get extra screening with ultrasound or MRI. That screening can find more cancers in dense breasts, but it can also lead to more false positives and needless surgery.

This study makes the point that women need to know not just about breast density, but what kind of breast density, and other risk factors, too.

Sounds complicated. So we called up Dr. Karla Kerlikowske, a professor of medicine at the University of California, San Francisco and lead author of the study, to help us figure this out. The conversation has been edited for length and clarity.

Your study looks at breast cancer risk using not just breast density but also family history, age and ethnicity. Why is that?

About 45 percent of women have dense breasts; that's a large number of women. But the sensitivity of mammograms is such that we're not missing 45 percent of cancers. So can we narrow it down to women who are at higher risk of cancer, and especially women at higher risk of advanced cancer? Then if we did supplemental imaging of women in that group, it might help them.

How would I figure out the other risk factors besides breast density?

You can use our Breast Cancer Surveillance Consortium Risk Calculator; it looks at age, race, family history, history of biopsy and breast density. Ours is the only risk calculator that has breast density in it. We actually validated it in another mammography population. And it's an app; just type in "BCSC Risk Calculator" and download.

I looked at the calculator, and even though I've been told I have dense breasts I realize I have no idea if they're heterogenous or extremely dense, which are the higher-risk categories. How do I find that out?

The provider who ordered the test will get that information. You'd have to ask the provider; it's in the mammography report. My understanding from the bills in Congress is that you'd actually be told what your density is; if you're fatty or scattered or heterogenous or extremely dense. All women would be informed, and they would know the category. If I have fatty breasts I'd like to know that, too, because then I'm at really low risk.

Are you telling your patients that?

It sort of depends. If I don't think they're at high risk of an interval cancer I tend not to worry them too much. If they're at high risk then I have a discussion with them. If they have fatty breasts I let them know, wow, you're really at low risk for cancer.

It feels like we're still struggling with who really needs the extra scans. How will we figure that out?

Now that we know who these high-risk groups are, we need to know how supplemental screening works in those high-risk groups. If we add ultrasound, do we miss less cancer? If we add MRI, do we miss less cancer? We have data on both of them, and we're in the process of analyzing them.

When will we find out?

I'm hoping sometime this summer.