What Is Breast Density, Exactly? Oncologists Explain

Breast density is a hot topic in women's health right now thanks to a new rule from the Food and Drug Administration (FDA) that went into effect in September. Under the rule, all women who get a mammogram will be given information about the density of their breasts.

But breast density isn't usually a topic that comes up at your annual ob-gyn visit or physical, making it understandable to have questions. So, what is breast density and what does having dense breasts mean for your cancer risk? Here's what oncologists want you to know.

Wael Harb, MD, is a hematologist and medical oncologist at MemorialCare Cancer Institute at Orange Coast and Saddleback Medical Centers in Orange County, CA.

Richard J. Bleicher, MD, is the chief of the Division of Breast Surgery at Fox Chase Cancer Center.

Breasts are made up of glandular tissue, fibrous connective tissue, and fatty breast tissue, according to the National Cancer Institute (NCI). The density of breasts describes the amount of these types of breast tissue that are seen on a mammogram, according to Wael Harb, MD, hematologist and medical oncologist at MemorialCare Cancer Institute at Orange Coast and Saddleback Medical Centers in Orange County, CA.

You can't tell if you have dense breasts just by feeling them — this is only determined by a mammogram, Dr. Harb says.

There are four categories of dense breasts to be aware of. Those include:

Breasts that fall into category C and category D are considered dense breasts.

It depends. "It's partly genetics and partly hormones," says Richard J. Bleicher, MD, chief of the Division of Breast Surgery at Fox Chase Cancer Center. Age can also play a role. "Breast tissue ends up becoming less dense with time," he says.

However, if a woman uses hormone replacement therapy in menopause, her breast density tends to stay more consistent, Dr. Bleicher says.

No, doctors say you shouldn't worry about having dense breasts. In fact, it's very common for women to have dense breasts, with nearly half of all women over 40 falling into this category.

"Women should definitely not worry about having dense breasts," Dr. Bleicher says.

While dense breasts aren't considered abnormal or a disease, there is a slightly higher risk of developing breast cancer if you have dense breasts, Dr. Bleicher says. That risk is independent from how having dense breasts impacts the ability to read a mammogram, according to the NCI.

Dense breasts can make a mammogram harder to read. "When we do a mammogram and we see density, it means that we might miss cancer," Dr. Harb says. "We have to consider other screening modalities if they have dense breasts, like ultrasound or MRI."

Currently, there are no special screening recommendations for women based on breast density alone. So, if you receive a mammogram that shows you have dense breasts, it's best to check in with your doctor about the possibility of additional screening.

"There may be recommendations for an ultrasound or MRI, in part dependent on your overall risk level for breast cancer," Dr. Bleicher says. "But there's not a uniform recommendation yet with respect to special screening for those with dense breasts. The most important thing is to talk to your doctor. "

Korin Miller is a writer specializing in general wellness, health, and lifestyle trends. Her work has appeared in Women's Health, Self, Health, Forbes, and more.