Breast Density and Its Role in Your Cancer Risk

If your mammogram report mentioned that you have "dense breasts," you are far from alone, and it is not a diagnosis. About 40 to 50% of those assigned female at birth (AFAB) over 40 years old have dense breast tissue.¹ Still, density is worth understanding, because it affects both your breast cancer risk and how well a mammogram can see through your tissue.

This guide explains what breast density means, how it is measured, how it relates to cancer risk, and what steps you can take if you do have dense breast tissue.

Breast density describes the mix of tissue in your breasts as it appears on a mammogram. Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Fibrous and glandular tissue (together called fibroglandular tissue) appear white on a mammogram, while fatty tissue appears dark. The more fibroglandular tissue you have relative to fat, the "denser" your breasts are.²

Importantly, breast density has nothing to do with how your breasts feel or their size or firmness; it is determined from a mammogram.²

Radiologists classify breast density using a system called BI-RADS, which has four categories.³ The last two are considered "dense."

Roughly 10% of women fall into category A, 40% into B, 40% into C, and 10% into D, which means about half of those who are screened have dense breasts.³

Dense breast tissue is an independent risk factor for breast cancer, and the risk rises with density.⁴ Research shows:

• Women with extremely dense breasts (category D) are about four to six times more likely to develop breast cancer than women with almost entirely fatty breasts.⁵

• Compared with women who have scattered density, those with extremely dense breasts have roughly twice the risk.⁴

It is worth keeping this in perspective. Dense breasts are common, and having them does not mean you will develop breast cancer. It simply means density is one factor your healthcare provider should weigh alongside your other risk factors.

Beyond raising risk, dense tissue creates a second challenge: it can hide cancer on a mammogram. Because both dense fibroglandular tissue and tumors appear white on the image, dense tissue can camouflage a growing cancer.⁶

This "masking" effect is significant. An estimated 40% of cancers may not be visible on a mammogram in extremely dense breasts, and about 25% may be missed in heterogeneously dense breasts.⁶ That is why people with dense breasts may benefit from additional screening beyond mammography alone. However, not everyone with dense breasts needs supplemental screening.

As of September 10, 2024, the U.S. Food and Drug Administration requires mammography facilities subject to federal MQSA requirements in the United States to tell patients whether their breasts are "dense" or "not dense" in their mammogram results.⁷ The goal is to make sure every woman has the information she needs to talk with her healthcare provider about her personal risk and whether additional screening makes sense.

A dense-breast notification is a prompt for a conversation, not a cause for panic. Helpful steps include:

• Keep up with regular mammograms. The USPSTF recommends screening mammography for women ages 40-74 every other year.⁸

• Talk to your healthcare provider about your overall risk. Density is one piece of the picture, alongside family history, age, and other factors.

• Ask whether supplemental screening is right for you. Depending on your risk, your provider may suggest an additional imaging test.

Potential supplemental screening options include:

Supplemental screening can find some cancers that mammography misses, but it can also lead to false-positive results and unnecessary additional testing. Talk with your healthcare provider about whether the potential benefits outweigh the harms for you.⁸

Yes. Breast density tends to decrease with age, especially after menopause.² Because density can change, it is worth checking your category on each mammogram report rather than assuming it stays the same.

If your mammogram report notes dense breasts, schedule time to talk with your provider about what it means for you, particularly if you also have a family history of breast cancer or other risk factors. And regardless of density, see a healthcare provider promptly if you notice a new lump, skin changes, nipple discharge, or other breast changes.

Dense breasts are very common.¹ They are associated with an increased risk of breast cancer and can make mammograms harder to read, which is why it is worth discussing your density and overall risk with your healthcare provider.⁴

Breast density can only be determined from a mammogram. As of September 2024, your mammogram report must tell you whether your breasts are dense or not dense.⁷

Not everyone with dense breasts needs supplemental screening. Whether it is recommended depends on your overall risk, so the decision is best made with your healthcare provider.⁸

Density is influenced largely by genetics, age, and hormones, and it generally decreases naturally after menopause. There is no proven way to intentionally reduce it, so the focus is on appropriate screening rather than changing density itself.¹

Understanding your breast density is one part of a proactive approach to your health, and understanding your overall risk is the next. Density is one of several factors that shape that risk, and your mammogram holds more information than a single density category.

The Clairity Breast™ Cancer 5-Year Risk Assessment, available through Everlywell, uses FDA-authorized AI-driven software to analyze patterns in breast tissue on a routine screening mammogram from the last 12 months and estimate your personalized five-year breast cancer risk. Provider-reviewed results are delivered to your My Everly account with guideline-based information to review with your healthcare provider, who may use your risk score to personalize your care plan, including whether supplemental screening or risk-reduction options make sense for you. That added context can help support earlier detection.

Clairity Breast estimates future risk. It does not detect or diagnose cancer, and it is not a substitute for mammograms or ongoing care with your provider. Keep up with recommended screenings, and talk with your healthcare provider about the screening plan that fits your density and your risk. Everlywell is here to help you stay proactive about your health.