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Appropriate imaging for breast cancer screening in special populations
There are two major policy considerations surrounding the use of advanced imaging approaches in breast cancer screening. The first is the potential for DBT to replace digital mammography as a frontline screening tool in asymptomatic women. Because this is a new technology, the evidence base is expected to be limited, particularly with respect to long-term patient outcomes.
The other major consideration relates to the use of supplemental screening among women with a normal mammogram (i.e., no abnormalities detected) but with dense breast tissue that might obscure an abnormality. Breast density is qualitatively assessed by the radiologist based on mammographic images into one of four possible letter designations: (a) almost entirely fatty, (b) scattered areas of fibroglandular density, (c) heterogeneously dense, which may obscure small masses; or (d) extremely dense, which lowers the sensitivity of mammography (Mercado, 2014). The term “dense breast tissue” has primarily been applied to categories (c) and (d).
Supplemental screening is a generally-accepted practice among women with very strong risk factors for breast cancer, such as BRCA mutations or a personal history of the disease. However, these represent a small proportion of screened women. In contrast, dense breast tissue is present in nearly 50% of adult women (ICER/CTAF, 2013). While the presence of dense breast tissue has also been acknowledged as an independent (although modest) risk factor for breast cancer and denser tissue may mask tumors on standard mammography, little is known about the potential impact of supplemental screening if it were to be expanded to all women with dense breast tissue regardless of overall breast cancer risk.
Nevertheless, within the last decade, 18 states have passed legislation requiring physicians to notify women if they have dense breast tissue, largely as a result of patient advocacy efforts fueled by situations of missed cancer on mammography (Are You Dense Advocacy, 2014). Some of these mandates also require insurers to cover supplemental screening in such women. Many patient advocacy groups have commended these efforts, stating historically poor communication between the medical community and patients about the limitations of mammography (Lee, 2013). Others are concerned that such mandates are premature, as the current literature does not provide evidence of the benefits of supplemental screening in such a large and diverse population (D’Orsi, 2012). Advocates for DBT have also stated that the three-dimensional visualization may obviate the need for supplemental screening in women with dense breast tissue, but there are questions about whether there is sufficient evidence to support this claim. Payers and policymakers alike are concerned about the level of benefit that might be gained from supplemental screening in this population relative to the potential harms of patient anxiety, overdiagnosis, and false-positive findings.
Primary criteria ranking
- Safety = Low
- Efficacy = High
- Cost = High
- Draft key questions published: July 15, 2014
- Public comment period: July 15 - July 29, 2014
- Final key questions published: August 22, 2014
- Draft report published: October 21, 2014
- Public comment period: October 21 - November 21, 2014
- Final report published: December 17, 2014
- HTCC public meeting: January 16, 2015
It is estimated that about one in eight women in the United States will develop invasive breast cancer in her lifetime; breast cancer is also the second-leading cause of cancer death among women, behind only lung cancer (BreastCancer.org, 2014). Some women have an elevated risk of breast cancer, including those who have a personal or family history of the disease, genetic abnormalities (particularly carriers of the BRCA1 and BRCA2 gene mutations), previous instances of chest radiation therapy, or the presence of denser, more fibrous breast tissue.
Early detection is widely considered essential to reduce the risk of breast cancer mortality. Population-based screening with x-ray mammography is considered the standard of care for women over 40 in the United States. Mammography has evolved from film-based to digitally reconstructed two-dimensional imagery, which has resulted in improved visual precision and better sensitivity (Pisano, 2005). However, even digital mammography results in some missed cancers and requires relatively large numbers of women to be “recalled” for additional screening and/or biopsy, most of who are ultimately judged not to have cancer (i.e., false positives). In 2011, the FDA approved the use of digital breast tomosynthesis (DBT), a three-dimensional form of mammography that has the promise of improved cancer detection and lower recall rates in comparison to digital mammography. In addition, the FDA’s recent approval of specialized imaging software has eliminated the need to generate 2D and 3D images separately, which in effect doubled the radiation dose to the patient. Now, 2D images can be generated directly from DBT data, and recent study suggests that results are comparable to the older combination procedure (Zuley, 2014). Despite this promise, however, questions remain about DBT’s performance over the long-term, its ability to discriminate between early aggressive cancers versus those tumors not likely to grow (i.e., “overdiagnosis”), as well as its characteristics in specific patient subpopulations.
Women who are at an increased risk of developing breast cancer (as described above) often undergo supplemental screening to allow a second opportunity to identify tumors. Imaging technologies used for this purpose typically include magnetic resonance imaging (MRI), as well as ultrasonography. Traditional ultrasounds are performed using a handheld wand, but a relatively new variant on this technology involves use of an automated transducer that also produces three-dimensional images (Kelly, 2011). As with DBT, there are also questions about the impact of these supplemental screening approaches on cancer detection, overdiagnosis, and false-positive rates.