Breast density is a significant yet often overlooked factor in breast cancer awareness, risk assessment and screening practices . Understanding what breast density is, how it affects breast cancer risk and what it means for screening can help women make informed decisions about their health.
Author
- Justin Stebbing
Professor of Biomedical Sciences, Anglia Ruskin University
Breast density refers to the proportions of glandular and connective tissue compared to fatty tissue in the breast, as seen on a mammogram . Simply put, dense breasts have more glandular and fibrous tissue and less fat.
On a mammogram, both dense tissue and tumours appear white, making it harder to detect abnormalities in women with dense breasts. This masking effect can lead to cancers being missed during routine screening, which is why breast density is not just a risk factor for developing breast cancer, but also for having it go undetected until it is more advanced .
Recent large-scale studies have confirmed that women with dense breasts face a higher risk of developing breast cancer compared to women with less dense, fattier breasts. For example, a major study involving more than 33,000 women found that those with dense breasts were nearly twice as likely to develop breast cancer than those with low breast density.
This increased risk is seen across both pre-menopausal younger women and post-menopausal older women, although the proportion of women with high breast density tends to decrease with age.
In practical terms , women with the lowest breast density have about a 6% lifetime risk of developing breast cancer after age 50, while those with the highest density face a risk closer to 15%.
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The impact of breast density on cancer detection is also significant . Mammography, the standard screening tool, is less sensitive in women with dense breasts. While mammograms can detect about at least nine out of ten cancers in women with mostly fatty breasts, the sensitivity drops to about seven out of ten in women with extremely dense breasts.
This means that tumors can be missed, leading to what are known as "interval cancers" , cancers that are diagnosed between regular screenings, often at a more advanced stage.
Supplemental screening methods, such as MRI scanning , can help detect cancers that mammography might miss in women with dense breasts, and some pilot studies have shown that additional cancers are found this way.
Breast density is now recognised as one of the most important risk factors for breast cancer, even as much as family history or other commonly discussed risk factors.
About 40% of women fall into the higher density categories, and dense breasts are common in younger women, those taking hormone replacement therapy, and those with certain genetic backgrounds and ethnicities . However, breast density can also be influenced by lifestyle and hormonal factors, and it tends to decrease with age and higher body mass index and obesity .
Given the importance of breast density, there has been a growing movement to ensure women are informed about their own breast density after mammograms, and to address this appropriately . A recent UK survey showed that most women aren't aware of their breast density .
In the US, new regulations require that all women undergoing mammography be notified if they have dense breasts and be advised about the associated risks. This aims to empower women to have more informed discussions with their healthcare providers about their personal risk and the potential need for additional screening.
Despite the increased risk, it is important to remember that the majority of women with dense breasts will not develop breast cancer. Breast density is just one factor among many, and decisions about screening and risk reduction should be made on an individual basis.
For women with dense breasts, discussing options for supplemental screening with their doctor is recommended. While there is currently no widely accepted intervention to reduce breast density, in my own research , I'm exploring new ways to address this risk factor.
In summary, breast density is both a common and significant risk factor for breast cancer, and it can complicate the detection of cancer through standard mammography.
Women should be aware of their breast density status, understand its implications for both risk and screening, and work with their doctors to determine the best approach for their individual situation. As awareness grows and screening practices evolve, the hope is that more cancers will be detected earlier, improving outcomes for all women.
Justin Stebbing does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
