By Will Boggs MD
NEW YORK (Reuters Health) - The percentage of digital mammography screens assessed as dense has remained steady with changes in Breast Imaging Reporting and Data System (BI-RADS) guidelines and implementation of digital breast tomosynthesis, according to findings from the Breast Cancer Surveillance Consortium (BCSC).
"Physicians should be aware that changes in mammography guidelines and technology have not resulted in dramatic changes in breast density assessment for the population as a whole," Dr. Brian L. Sprague from the University of Vermont in Burlington told Reuters Health by email. "However, this does not mean that specific radiologists have not changed their density assessment practice in response to the new BI-RADS guidelines."
The 2003 BI-RADS 4th edition categorized breast density based on the visual assessment of the percentage of fibroglandular tissue within the breast, but the 2013 BI-RADS 5th edition omitted this percentage-based system and emphasized an assessment of the potential for the masking of suspicious lesions behind dense tissue. This change could result in women with small areas of focally dense tissue being categorized in a higher density category.
Half of U.S. facilities now have digital tomosynthesis (DT) units (first approved in 2011), which some studies have suggested may be less likely to classify breasts as dense compared with digital mammography (DM).
Dr. Sprague and colleagues investigated temporal trends in clinical breast density assessment among 2,990,291 DM screens and 221,063 DT screens interpreted by 722 radiologists from 144 facilities in the BCSC.
After age standardization, 46.3% of DM exams had dense breasts during the BI-RADS 4th edition era, compared with 46.5% during the BI-RADS 5th edition era, according to the January 8th online report in the Journal of the National Cancer Institute.
Among exams conducted during 2014-2016, 45.8% of DT exams had dense breasts, compared with 46.5% of DM exams.
The distributions of the four density categories were also similar for DM exams during the two edition time periods and for DM and DT exams during 2014-2016.
"Our findings parallel prior observations that there was no substantial change in the distribution of breast density categories in the BCSC after the addition of the percentage-based guidance in the BI-RADS 4th edition in 2003 or during the transition from film to digital mammography," the researchers note. "Similarly, our findings suggest that the widespread implementation of digital breast tomography in U.S. clinical practice has not substantially affected density assessment."
"Physicians should continue to be aware that density assessment in most clinical practices remains a subjective task that is subject to widespread variability across radiologists," Dr. Sprague said. "Women and their physicians should consider breast density as one of many relevant factors when considering breast cancer screening and prevention options."
Dr. Stamatia Destounis from the University of Rochester, New York, who has researched various aspects of screening and diagnostic breast imaging, told Reuters Health in an email, "Currently, 36 states in the U.S. have 'mandated reporting,' where the radiologist is required by law to reveal to a woman her breast density after receiving a mammogram. With nearly half of all women undergoing screening mammography receiving results that they have dense breast tissue, this is quite a large number of women hearing they have dense breasts. Unfortunately, the wording and level of explanation in the report to these women are not always clear. Many women are left confused about what it means to have dense breasts."
"Often women turn to their primary care doctors and gynecologists for answers," she said. "It is very important for these doctors to clearly understand the implications of dense breasts. Dense breast tissue is normal, and more common in younger women. Dense breast tissue is an independent risk factor for breast cancer in and of itself, but also the greater percentage of glandular tissue in the breast lends to a masking effect on a mammogram. Glandular tissue shows up white on a mammogram, as do cancers. Therefore, when a woman has dense breasts with a larger amount of dense tissue, that tissue can hide a cancer, delaying a diagnosis."
"Therefore, it is important for both doctors and patients to know there are supplemental screening options for women with dense breasts," Dr. Destounis said. "Screening ultrasound, both handheld and automated, allows radiologists to see through dense tissue and to possibly catch a lesion that was missed on the mammogram due to the masking effect of dense tissue."
"As the prevalence of dense breast tissue is staying steady, physicians need to ensure they are prepared to have conversations regarding the meaning and screening options for dense breasts," she said. "Patients can now investigate dense breasts for themselves with the plethora of information available on the internet; however, being able to successfully understand that information and make the best decisions for themselves will require an open and personal conversation with their own healthcare professionals."
J Natl Cancer Inst 2019.
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