What You Need to Know about Breast Tissue Density

In March 2014, Susan Landay had a routine mammogram, just as she had done for the past 10 years. The 50-year-old Newton resident had never had a breast problem, and there was no history of breast cancer in her family. So imagine her surprise when, one week after her mammogram showed nothing unusual, she felt something odd in her breast.

"At first I figured everything was probably okay if my mammogram was normal," Sue says. "I forgot about it for a while, but then it didn't go away and it didn't feel right."

Several weeks later, Sue underwent a breast ultrasound at Beth Israel Deaconess Medical Center, which highlighted the area of concern. She immediately had a biopsy and soon after was diagnosed with breast cancer.

Tejas Mehta, MD, MPH, Chief of Breast Imaging and co-Director of the BreastCare Center at BIDMC, later looked at Sue's initial mammogram and told her that the lump was indeed "impossible to see." Sue's mammogram did show dense breast tissue, which is why the cancer was not detected.

"I remember seeing in the mammogram report the words 'no evidence of malignancy,'" Sue says. "After my diagnosis, I re-read the findings on the report, which did mention that my breast tissue was extremely dense. But I didn't see it as unusual or as any kind of warning — I had assumed that if my GYN felt I needed further care, he would be in touch."

Dense breast tissue is not unusual — about 50 percent of women in the U.S. have dense breasts, according to the American College of Radiology, meaning there is more fibrous tissue in their breasts than fatty tissue. However, recent studies have found that having dense breast tissue may increase the risk of breast cancer relative to women with only fatty tissue.

Dense breast tissue appears white on a mammogram, as do masses — both benign and cancerous — meaning mammograms can be less accurate in detecting breast cancer if a woman has dense breasts.

"Breast tissue density is determined by the radiologist who reads a patient's mammogram," Mehta explains. "There are four categories of breast density, ranging from almost all fatty — the least dense — to all fibrous. About 10 percent of women are classified as having 'extremely dense' breast tissue. A woman's individual level of density can vary due to weight and hormonal changes. Density may also decrease with age — younger women tend to have denser breast tissue than older women."

The aim of a new law in Massachusetts, which went into effect on January 1, 2015, is to help women understand what it means to have dense breast tissue. The law requires all mammography service providers to give every patient an explanation of the degree of her breast density, as well as general information about how dense breast tissue can potentially interfere with detection of breast cancer on a mammogram.

Mehta says that although the law has good intentions, it has created a little confusion for both patients and doctors, because there are no additional guidelines as to what a woman should do next if she is found to have dense breast tissue. The law only states that additional breast screening 'may be advisable,' and that the patient should discuss her mammogram results with her primary and referring physicians, as well as with the radiologist who reads her mammogram.

Supplemental screening exams, if thought to be necessary, include 3-D mammography (tomosynthesis), breast MRI, and whole breast screening ultrasound. But, according to Mehta, insurance companies don't always cover supplemental screenings, and a patient's individual risk for breast cancer — which can sometimes be tough to determine — often comes into play.

"The best thing to do is to talk with your doctor about your personal and family medical history to see if there is anything that could increase your breast cancer risk," Mehta says. "Many doctors think that most women who have dense breasts without other risk factors may not need any additional screening exams. If your mammogram shows that you have dense breasts, it may come down to doing what you are most comfortable with."

Regardless of breast density, routine mammography remains the best and most important imaging exam to screen for breast cancer, Mehta adds. Women who have a high risk of breast cancer should also speak with their doctor about other screening options or starting screening at an earlier age.

Sue, who is doing well and feeling great after undergoing cancer treatment at BIDMC, knows how fortunate she is to have found the undetectable mass, and hopes that the new law will help more women understand what breast density means. (More than 20 states have enacted similar laws in recent years.)

"I'm really glad that awareness is being raised for both patients and doctors," she says. "You rely on your health providers to tell you if you need further testing. Maybe if I knew more about breast density and the unreliability of mammograms for people like me, I would have acted a little faster when I felt something in my breast.

"At this point, I feel lucky that I found the cancer, and I had about an easy time as I possibly could have in being treated," she adds gratefully. "I appreciate that BIDMC recognizes that breast cancer isn't the same from woman to woman, treatment is not one-size-fits-all, and I'm also incredibly lucky to have had access to such amazing doctors right from the get-go."

Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.

Posted May 2015