Scientists have long known that dense breast tissue is linked to an increased risk of breast cancer in women, but a recent study adds a new twist, finding that while breast density declines with age, a slower rate of decline in one breast often precedes a cancer diagnosis in that breast.
Scientists at Washington University analysed breast density changes over a 10-year period in 10 000 women who were cancer-free when the study started. Some 289 of them were diagnosed with breast cancer in that time; the study compared changes in their breast tissue to those in 658 similar women who did not develop breast cancer.
Breast density was higher from the start in the women who went on to develop breast cancer, and density declined in all women over time. But when each breast’s density was measured separately, the researchers found a significantly slower decline in density in breasts that developed cancer, compared with the other breast in the same patient, reports The New York Times.
Why it matters
Shu Jiang, the study’s lead author and an associate professor of public health sciences at Washington University, said the findings might provide an individualised and dynamic tool for assessing a woman’s breast cancer risk. “I hope they can get this into clinical use as soon as possible – it will make a huge difference,” she said. “Right now, everybody only looks at density at one point in time.”
However, women have mammograms at regular intervals throughout their lives, and the density of each breast is measured each time.
“So this information is actually already available, but it’s not being utilised,” she said. Now, a woman’s risk of developing breast cancer could “be updated every time she gets a new mammogram”.
Breast density is now an acknowledged risk factor for breast cancer, albeit one of many. Dense tissue also makes tumours harder to detect in imaging scans.
Dozens of states have started requiring mammography centres to notify women if they have dense breast tissue. In March, the US Food and Drug Administration recommended that providers tell women about their breast density.
But this is the first study to measure changes in density over time and to report a link to breast cancer.
Though larger studies will need to be done to confirm the findings, Karen Knudsen, chief executive of the American Cancer Society, called the data “exciting”.
“This is the first study I’ve seen that looks specifically across time at changes from breast to breast, instead of averaging the two breasts, where you might miss these changes,” she said.
Although women are provided with the information about breast density and the risks associated with it, the study suggests that information could be better used. “We need to know how to follow women with dense breasts, instead of just alerting them,” Knudsen said.
One next step may to be examine breast density over time – in women taking medication to prevent breast cancer – to see if the density decreases, she suggested.
“There could be different risk stratification guidelines set up to monitor those who are having much slower decline in tissue density, versus those who are not,” Jiang said.
Study details
Longitudinal Analysis of Change in Mammographic Density in Each Breast and Its Association With Breast Cancer Risk
Shu Jiang, Debbie Bennett, Bernard Rosner, et al
Published in JAMA Oncology on 27 April 2023
Key Points
Question Is change in mammographic breast density associated with the development of breast cancer, and does this change diverge from the expected decrease in density with age?
Findings In this nested case-control cohort study of 947 women attending breast screening during up to 10 years, a decrease in breast density was observed in all women regardless of subsequent breast cancer development. The rate of density change was significantly slower in the breast in which cancer was later diagnosed.
Meaning This study found that evaluating longitudinal changes in breast density from digital mammograms may offer an additional tool for assessing risk of breast cancer and subsequent risk reduction strategies.
Abstract
Importance
Although breast density is an established risk factor for breast cancer, longitudinal changes in breast density have not been extensively studied to determine whether this factor is associated with breast cancer risk.
Objective
To prospectively evaluate the association between change in mammographic density in each breast over time and risk of subsequent breast cancer.
Design, Setting, and Participants
This nested case-control cohort study was sampled from the Joanne Knight Breast Health Cohort of 10 481 women free from cancer at entry and observed from November 3, 2008, to October 31, 2020, with routine screening mammograms every 1 to 2 years, providing a measure of breast density. Breast cancer screening was provided for a diverse population of women in the St Louis region. A total of 289 case patients with pathology-confirmed breast cancer were identified, and approximately 2 control participants were sampled for each case according to age at entry and year of enrolment, yielding 658 controls with a total number of 8710 craniocaudal-view mammograms for analysis.
Exposures
Exposures included screening mammograms with volumetric percentage of density, change in volumetric breast density over time, and breast biopsy pathology-confirmed cancer. Breast cancer risk factors were collected via questionnaire at enrolment.
Main Outcomes and Measures
Longitudinal changes over time in each woman’s volumetric breast density by case and control status.
Results
The mean (SD) age of the 947 participants was 56.67 (8.71) years at entry; 141 were black (14.9%), 763 were white (80.6%), 20 were of other race or ethnicity (2.1%), and 23 did not report this information (2.4%). The mean (SD) interval was 2.0 (1.5) years from last mammogram to date of subsequent breast cancer diagnosis (10th percentile, 1.0 year; 90th percentile, 3.9 years). Breast density decreased over time in both cases and controls. However, there was a significantly slower decrease in rate of decline in density in the breast that developed breast cancer compared with the decline in controls (estimate = 0.027; 95% CI, 0.001-0.053; P = .04).
Conclusions and Relevance
This study found that the rate of change in breast density was associated with the risk of subsequent breast cancer. Incorporation of longitudinal changes into existing models could optimise risk stratification and guide more personalised risk management.
See more from MedicalBrief archives:
FDA sets new rules for dense breasts cancer warning
Dense breasts a high risk of cancer – US study
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