Starting Mammograms at Age 40 Could Help Track Important Breast Density Changes

Higher breast density has long been linked with a greater risk for breast cancer. In fact, among people between the ages of 40 and 49, dense breasts are associated with a two-fold greater risk of cancer.

Now, new draft guidance from the U.S. Preventive Services Task Force recommends that all women should start getting regular mammograms at age 40 instead of 50.

The suggested guidance coincides with new findings about the link between cancer risk and breast density.

The new study, published last month in JAMA Oncology, was the first to track changes in breast density over time. While breast density typically declines with age, a slower decline in one breast may indicate a higher risk of cancer. Beginning mammograms at a younger age would allow providers a larger window of time to monitor density changes and assess breast cancer risk.

Cancer Can Impact an Individual Breast

Cancer rarely develops in both breasts at the same time; only about 3% of women have bilateral cancer. While all of the 947 JAMA study participants experienced a decrease in breast density over the study period, in the 289 women who developed cancer, the affected breast had a slower change in breast density.

The researchers analyzed a decade’s worth of mammograms to show that women with higher breast density at the start of the study had a greater likelihood of developing breast cancer throughout the decade.

The findings could be used to help clinicians determine when women are at higher risk of cancer and to pay special attention to the individual breast with a slower decline of tissue density, Shu Jiang, PhD, lead author and an associate professor of public health and Director of the Epidemiology and Biostatistics Cancer Imaging Research Center at Washington University School of Medicine, told Verywell.

“Each time a woman has a new mammogram taken, that information, plus all her past history of mammograms or density estimated before today’s mammogram, would be utilized to estimate her future risk of breast cancer,” Jiang said.

Jiang’s findings were not the basis for the new task force draft recommendations. But they offer insight into what exactly providers should monitor if they had more time to do so.

Why Breast Density Plays Role in Cancer Risk

Breast density refers to the amount of glandular and fibrous tissue relative to the fatty tissue in a person’s breasts. It’s measured on a four-point scale defined by the Breast Imaging Reporting and Data System (BI-RADS). About half of women older than 40 years have dense breasts.

When breast tissue is dense, it’s more challenging for radiologists to pinpoint tumors in a mammographic image. That can lead to some cancers going undetected. In March, the Food and Drug Administration (FDA) announced a requirement for mammography centers to notify women who were found to have dense breasts.

Breasts usually become less dense with age, and scientists aren’t exactly sure why. Apart from the imaging challenges, research indicates there is also some unknown biological process that makes breast density a risk factor for cancer, Maxine S. Jochelson, MD, a radiologist and Chief of the Breast Imaging Service at Memorial Sloan Kettering, told Verywell. Jochelson was not affiliated with the study.

The study authors excluded mammograms taken within six months of participants’ cancer diagnosis because their breast density could have increased due to undetected cancer.

Who Is Most Likely to Have Dense Breasts?

A younger age isn’t the only risk factor for dense breasts. Black women tend to have denser breasts than women of other racial and ethnic groups in the U.S.

About 80% of the participants in this study were White, while 14% were Black. Jiang said that group wasn’t big enough to know if there were meaningful differences in breast density or cancer risk by demographic.

“Ideally, we would be able to validate this in different cohorts with different ethnicity makeups to see if the result holds in different populations,” Jiang said.

How Tracking Density Over Time Could Inform Screening

Clinicians already take mammograms of both breasts. Typically, Jiang said, they will refer to past mammograms to see how a woman’s screenings have changed over time. They do this by “eyeballing” the change in breast density and mammography findings, rather than using a specific model.

“Right now, it is only today’s mammogram that’s being used to predict a woman’s future risk,” Jiang said. “We’re trying to say that you can use her past history of mammograms or density estimates to supplement today’s estimate.”

The researchers compared the participants’ rate of change in breast density to the average change in a control group. Jiang said that if put into clinical practice, providers could also compare a patient to a reference.

If more research validates this approach, Jiang said health providers could use this information to help predict a patient’s risk of breast cancer years in advance.

Jochelson said that the findings could help scientists understand the many complex factors that play into how and why breast cancer develops. In practice, though, she said these findings won’t likely change how clinicians diagnose or treat breast cancer.

For instance, while clinicians could selectively screen a breast that shows slower density decline, they’ll likely continue to image both breasts, Jochelson said. Besides, most treatments are systemic, meaning they affect both breasts equally. If a patient is determined to be at high risk for breast cancer, their clinician may give them tamoxifen, a hormone therapy that can prevent or slow cancer development.

It’s not yet clear how breast density stacks up with other key risk factors, like BRCA mutations or a patient’s family history. There are multiple risk models that can be used to predict a patient’s cancer risk.

But Jochelson said cancer can occur even in low-risk, otherwise healthy patients. Receiving routine screening is the best way to capture cancer early on.

“At the end of the day, with all the risk models and everything else, the highest risk for developing cancer is being a middle-aged woman,” Jochelson said.