The density legislation is here to stay and is likely to become more widespread. Whether you agree with this legislation or not, this is the playing field in front of us, and as such, we should look at this as an opportunity to institute thorough risk assessment.— Kevin Hughes, MD
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Dense breasts are not an automatic indication for additional imaging. Instead, breast density generally provides an opportunity for improved risk assessment, according to Kevin Hughes, MD, of Massachusetts General Hospital, Boston. “More than 20 states have mandated that women be informed of their breast density. This has caused confusion among patients and consternation among physicians,” he noted.
The legislation in the state of Massachusetts reads: “Every provider of mammography services shall, if a patient’s mammogram reveals dense breast tissue, as determined by the interpreting physician based on standards promulgated by the American College of Radiology, provide written notification to the patient, in terms easily understood by a lay person.” This is a tall order, since even many clinicians do not fully understand breast density, said Dr. Hughes, Co-Director of the Avon Comprehensive Breast Evaluation Center and Medical Director of the Bermuda Cancer Genetics and Risk Assessment Clinic.
Dr. Hughes clarified the fine points related to breast density and risk at the 2016 Miami Breast Cancer Conference.1 Referring to the concerns with dense breasts, he explained that density does decrease the sensitivity of mammography, but much less so with modern digital and tomosynthesis (3D) mammography. Density may increase risk, he added, but it is dependent on the age and body mass index of the patient.
What Is a ‘Dense’ Breast?
Developed by the American College of Radiology, the BI-RADS (breast imaging reporting and data system) categories now stratify patients as A, B, C, or D. In these subgroups, category A is almost entirely fatty (10%), B shows scattered areas of fibroglandular density (40%), C is labeled heterogeneously dense (40%), and D is considered extremely dense (10%). Categories C and D are considered “dense,” but patients in category B mistakenly assume their breasts are dense as well because the word appears in the description.
With 50% of the population in the actual dense breast group, “it’s hard to use this as a differentiator, since anything that picks up 50% of the population is probably not going to be overly useful,” admitted Dr. Hughes.
Factors That Confound Risk
“Increased density can mask cancer on a mammogram, and increased density is related to some degree to increased risk, but it’s not a simple one-to-one relationship,” Dr. Hughes said. Although the sensitivity of film-screen mammography declines as density increases, the same reduction in sensitivity does not occur with digital mammography. Therefore, digital mammography may have solved some of this problem, he added.
Both whole-breast ultrasound and tomosynthesis can identify additional cancers in women with mammography-negative dense breasts, according to a recent adjunctive screening trial in which ultrasound identified an additional 7 and tomosynthesis an additional 3 cancers per 1,000 patients.2 “Tomosynthesis did a good job in identifying at least half the occult cancers, and ultrasound did even better; however, it’s not clear that the additional costs and difficulties of ultrasound are cost-effective, so whole-breast ultrasound is still controversial,” indicated Dr. Hughes.
A “more interesting part of the equation” is the relationship between density and cancer risk, as it is not uniform, he continued. Asian women have higher breast density but a lower cancer risk; young women have higher breast density but a lower short-term risk than older women; older women with a high body mass index have low breast density but a higher breast cancer risk; and breast density declines with age, although cancer risk increases.
Lower body mass index in Asian women partly explains their higher breast density. The breast has a uniform amount of tissue, and “the size of the envelope” determines how dense this looks on mammography. “In a small envelope, breasts look denser than in a large envelope,” he explained.
Breast Density and Cancer Screening
- Legislation in 20 states mandates that patients be informed if mammography indicates “dense breasts,” ie, categories C and D on BI-RADS.
- Breast density may mask cancer, but it is increasingly unlikely in the era of digital mammography.
- Cancer risk related to breast density must also take into account body mass index and age, which are related to risk.
- All patients, not just those with dense breasts, should be assessed for their lifetime risk of cancer and screened accordingly.
“Density is a function of both body mass index and age,” he concluded. “Just saying that density correlates with risk is not enough…. Actually, most of the density can be predicted by age and body mass index, and if you are predicting this way, it [density] does not have much of an effect on the risk of an individual patient.”
The “density residual” offers a better way of considering density in relationship to risk. This is the magnitude of difference between density found on mammography vs density predicted based on the patient’s age and body mass index. In other words, the residual is the density identified on mammography minus the density that is expected. A higher density residual is predictive of greater risk.
Warwick et al have refined the Tyrer-Cuzick risk model by incorporating the density residual into the calculation of risk.3 The updated model, which will be available soon, “will be a way to use density to predict risk in a way that makes sense,” he added.
Opportunity for Better Risk Assessment
“The density legislation is here to stay and is likely to become more widespread. Whether you agree with this legislation or not, this is the playing field in front of us, and as such, we should look at this as an opportunity to institute thorough risk assessment,” Dr. Hughes suggested.
Regardless of density, all women, especially younger women, should undergo breast cancer risk assessment. “The emphasis on density enables us to refocus on breast cancer risk,” he explained. “This will allow us to markedly improve on the number of women undergoing genetic testing and help to improve the rate of screening by MRI [magnetic resonance imaging] based on the American Cancer Society and NCCN [National Comprehensive Cancer Network] guidelines.”
More than 90% of women with hereditary cancer mutations are not aware of their risk, 99% of women needing breast screening MRIs are not getting them, and more than 66% of women who undergo breast screening MRIs are not eligible, he indicated.
What Are the Recommendations?
“In the era of breast density legislation, your patients will ask you what breast density means and what they should do about it. Remember, you don’t simply take density alone and translate that into risk for the individual. You need to do a thorough risk assessment to identify her level of risk,” emphasized Dr. Hughes.
The first question is whether a patient is at risk for a genetic mutation. If so, genetic testing is prudent, regardless of density. If not, but she has a > 20% lifetime risk (by Tyrer-Cuzick or another model), then regardless of density, she should receive routine mammography plus adjunctive MRI (or alternative adjunct, if necessary), starting at age 30.
For patients with < 15% lifetime risk, whether dense or not, routine mammography appears adequate. The controversial area is for patients with a 15% to 20% lifetime risk. “If they have dense breasts, we are not sure what to do,” he acknowledged.
Dr. Hughes recommended that patients in this group without dense breasts receive routine mammography; those with dense breasts should undergo routine mammography, and discuss with their physician whether adjunctive screening is necessary.
“Despite density legislation bringing density into the forefront, we need to bring risk assessment in general into the forefront and not just related to density,” Dr. Hughes emphasized. ■
Disclosure: Dr. Hughes has served on the speakers bureau for Myriad Genetics, is a shareholder in 5AM Solutions, and founded Hughes Risk Apps, LLC.
References
1. Hughes K: Breast cancer risk estimate in the era of density legislation. 2016 Miami Breast Cancer Conference. Surgical Oncology Track. Presented March 11, 2016.
