It is a theme that we have addressed several times in Salute Seno, that of dense breasts. Because it represents a risk on two fronts: it increases the probability of developing a tumor and, at the same time, it reduces the possibility that the mammogram can see it. With the help of Peter PanizzaHead of Radiology specializing in breasts at the San Raffaele Hospital in Milan, we try to answer some of the most frequently asked questions.
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What is meant by “dense breasts”?
The breast – or, more scientifically, the breast – has three components: the glandular tissue formed by the lobules (groups of acini) and the milk ducts, the fibrous tissue which acts as a “support scaffold”, and the adipose tissue, i.e. the fat. We can imagine the fibrous tissue as the branches of a tree and the glands as its leaves. In dense breasts we find a high percentage of glandular and fibrous tissue. Once it was thought that dense breasts were typical of youth, while today it is known that this characteristic frequently persists even in menopause.
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How do you tell if a breast is dense?
Mammographic density is a real parameter used by radiologists, and in fact the correct definition is “dense breast on mammography”. To date, only mammography can show if a woman has dense breasts: glandular and fibrous tissue appear, in fact, white on X-rays (they are said to be radio-opaque), while fat is easier to pass through and appears gray (radio-transparent).
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Is it true that mammography is less effective at detecting dense breast cancer?
Yes, because the nodules appear white (radio-opaque) just like the glandular and fibrous tissue, and the contrast of the mammographic image may not be sufficient to detect them. In fact, in breasts with a predominantly adipose component, the sensitivity of mammography, i.e. its ability to identify a tumor, is around 88%, while it drops drastically in dense breasts, where it can be reduced up to 60-65%.
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What does this imply?
Mammography remains the best test we currently have for screening, but women need to be aware that some cancers, especially in dense breasts, may go undetected on examination. This shouldn’t create alarmism, but awareness is important.
In the US it has become a legal obligation to inform women of their degree of density when they undergo mammography, thanks to the advocacy battle waged by the American patient and activist Nancy M. Cappello. She had fallen ill in 2003 with breast cancer and the mammography had failed to identify the lump. As reported by the New York Times, Nancy Cappello “turned her misfortune into a tireless campaign that led all states to more complete communication to women about the results and limits of their mammography” in case of dense breasts. Her story can be found on the website of the “Are you dense?” founded by her.
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Should mammograms and ultrasounds be done in the same session when the breasts are dense?
To compensate for the loss of sensitivity of mammography in dense breasts, this is associated with breast ultrasound, which represents the fibrous and glandular component as white and the nodule as gray, tending to black (offering greater contrast). Ultrasonography is therefore used as a follow-up test to mammography, especially in dense breasts. By observing mammography and breast ultrasound together, it is possible to recover a good percentage of sensitivity. Therefore, in dense breasts, if mammography and ultrasound are not done in the same session, an incomplete examination is performed.
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However, it must be said that ultrasound depends a lot on the experience of the operator who performs it and can give false positive cases (dubious/suspicious images that prove not to be pathological) and false negatives (i.e. it does not recognize lesions that are present), for which it is essential to always go to specialized centers for breast cancer, which ensure the expertise of those who carry out the examination. It should also be said that in these cases it is possible to resort to other tests in addition to ultrasound, as specified later.
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How is breast density measured?
The American College of Radiology (ACR) BI-RADS classification has 4 categories of breast density, from A to D. A corresponds to a low amount of radio-opaque glandular tissue on mammography, ranging from 0% to 25% (almost completely fat, affects about 10% of women); B between 25% and 50%; C between 50% and 75% (we say “heterogeneously dense” breasts, it concerns about 40% of women); D over 75% (“extremely dense” breasts, affects about 10% of women).
Is it true that having dense breasts increases the likelihood of developing cancer?
Yes, that’s why studies are underway to tailor the frequency and type of screening mammography exams based on various risk factors, including density category.
Has attention to breast density increased?
Very. So much so that since 2022 the World Dense Breast Day has also been established, which falls on the last Wednesday of September. Furthermore, in March of that same year, the recommendations of Eusobi (the European Society of Breast Imaging) for screening in women with extremely dense breasts were published in Breast. These are mainly based on the results of the Dutch DENSE study, published in the New England Journal of Medicine in 2019, which highlighted how Breast Magnetic Resonance (RMM) in dense breasts has a much greater sensitivity than mammography.
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What tests can be useful in the case of extremely dense breasts?
As mentioned, in Eusobi’s recommendations Magnetic Resonance is recommended in particular, which involves the intravenous injection of a drug, i.e. the contrast medium. Several studies are also underway on a relatively new method: mammography with contrast-enhanced mammography (CEM, from Contrast-Enhanced Mammography), which does not require any instrumentation other than the digital mammography provided in most Breast Centers (it is sufficient dedicated software). In this case, the contrast medium injected into the vein is iodine-based, the same used for CT scans. As in the case of Magnetic Resonance, the contrast medium accumulates where there is greater vascularization, bringing out any lesion that appears white while the rest of the breast is black.
Currently, the use of CEM is still not widespread, basically because it has not been included in the LEA (Essential Levels of Assistance) and therefore not recognized and reimbursed by the National Health System and by most of the Regional Health Systems.
In any case, in extremely dense breasts, if MRI and CEM are not available, ultrasound is still recommended to complete the mammography.