The New Breast Rating You Need to Know

Some experts say all women should be aware of their breast density—because a high number means you’re at increased risk of breast cancer 

by Joan Raymond
woman looking at her breast illustration image
Photograph: Illustrated by Aad Goudappel

Like many other women, I have a love-hate relationship with my breasts. Sure, they could nourish an infant, they’re a go-to destination for sexual arousal, and most important, they’re healthy. But my breasts are small, barely a B-cup, which would be fine if I were a supermodel. In reality, I’m a slightly plump, middle-aged woman who wears padded bras to avoid looking like a box when I put on a sweater. The silver lining: My breasts are perky, aka firm. And that firmness led me to assume that they are, in medical parlance, dense.

So I was surprised when I learned, from the radiologist’s report on my most recent mammogram, that my breasts aren’t all that dense. In fact, they are categorized as a bit fatty. Which in this case is a good thing.

Knowing your density matters because it can affect your odds of getting breast cancer. For women with the densest breasts, the chance of developing the disease is four to six times as high as it is for those with the least dense breasts. As a risk factor, density is third in importance, coming behind gender (being a woman) and age (the older you are, the higher your chances of getting breast cancer), says Karla Kerlikowske, MD, professor of medicine, epidemiology and biostatistics at the University of California, San Francisco.

You can’t look in the mirror and figure out your density. The determining factor is how much of your breasts consists of fibroglandular tissue (the milk ducts and the fibrous tissues that support them) and how much of fat tissue. About 10 percent of women have -extremely dense breasts (more than 75 percent fibroglandular tissue), and 40 percent have fairly widespread density (51 to 75 percent fibroglandular tissue), according to the American College of Radiology. Of the rest, 10 percent have almost completely fatty breasts, and 40 per-cent have only scattered areas of density.

Most women, after a normal mammogram, receive a letter that says “Congratulations!” and also gives their breast-cancer risk assessment. But some breast-cancer activists are calling for mammogram reports to give women more information. As of this writing, five states—New York, Connecticut, California, Virginia and Texas—have mandated that mammography providers inform women of their density in a written report and advise women with dense breasts that they may benefit from additional testing via ultrasound and MRI. (In other states, you can find out your density by asking your physician or radiologist.) Here’s what you need to know about why some experts and activists think breast density is so important.

The cancer connection
On a mammogram, fat looks gray-black, and normal fibroglandular tissue, malignant lesions and some benign conditions look white. A radiologist examines the proportion of gray-black and white on the mammogram image and categorizes breast density, typically assigning a BI-RADS (short for Breast Imaging-Reporting and Data System) composition classification. In this system, number 1 refers to the fattiest breasts, and number 4 the densest. (Don’t confuse the BI-RADS composition scoring with the BI-RADS assessment number, which runs from 0 to 6 and indicates your risk of having cancerous cells based on your mammogram results.)

The BI-RADS composition number sounds solid and scientific, but there’s one problem: It is “very subjective,” says Peter M. Jokich, MD, director of breast imaging at Rush University Medical Center in Chicago. Observational studies reveal that a radiologist, when shown the same breast image at various times, may categorize the image differently, giving it a BI-RADS 2 classification at one point and a BI-RADS 3 at another. “Doctors are good at classifying very fatty breasts and very dense breasts, but sometimes it’s more difficult for women whose breasts are somewhere in the middle,” explains Jokich. The middle matters because, according to one study, the risk of breast cancer increases as breasts become denser. In theory, then, women with a BI-RADS score of 3 (51 to 75 percent fibroglandular tissue) would have higher odds of getting cancer than women with a BI-RADS 2 score (25 to 50 percent fibroglandular).

Share Your Thoughts!


Cheryl Barker10.14.2013

Great info. Sounds like hospitals definitely need to start including the density numbers on mammogram reports. Maybe we can specifically request it when we go for our next mammograms.

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