Readers React: In defense of breast density notification laws
We read with interest the article “Breast density laws: Are you in compliance?” [December 2016 Contemporary OB/GYN]. We appreciated the perspective of our gynecologist colleagues. We would like to help clarify and give context to some of the information in the article.
Breast density notification laws were developed and enacted specifically because of strong evidence about the limitations of mammography in women with dense breast tissue and the demonstrated benefits of supplemental screening in them. The laws vary by state, although there are efforts to develop a national standard. It is important that radiologists, primary care physicians, and ob/gyns work together to implement breast density notification as effectively as possible.
The authors state, “These [breast density notification] laws … in general … are not supported by known clinical facts.” Later, they state, “The American College of Obstetricians and Gynecologists (ACOG) Committee Opinion 625 … relates that … no studies have demonstrated earlier detection or improved prognosis when additional breast imaging is obtained in patients with mammographically dense breasts.” It is important to revisit the literature, because increasingly strong evidence supports supplemental screening.
Randomized controlled trials have proven reduction in breast cancer mortality due to mammography screening.1-3 Importantly, the trials in which screening produced a shift to diagnosis of earlier-stage breast cancer, especially node-negative invasive cancer, are the ones that demonstrated improved outcomes.4,5 However, not all women benefit equally from mammographic screening. Interval cancers are those detected because of symptoms (such as a lump) during the interval between recommended screens. An interval cancer rate of more than 10% of cancers detected suggests the screening strategy is inadequate. In women with dense breasts, the interval cancer rate after mammographic screening is often more than 30% of all cancers, versus less than 10% in women with fatty breasts. Other modalities that improve detection of node-negative invasive cancer and reduce the interval cancer rate in women with dense breasts are expected to improve patient outcomes. Unfortunately, long-term mortality trials of supplemental screening would be prohibitively expensive and suffer from technology migration.
Benefits of screening mammography are reduced in women with dense breasts.6 Women with dense breasts are more likely to develop breast cancer, and breast cancer without calcifications can be masked by areas of dense tissue.7
Case 2 presented in the December article is an unlikely scenario because calcifications would typically be seen early (often in ductal carcinoma in situ component) even in dense breasts.
Earlier cancer detection by supplemental MRI
Based on multiple prospective international studies, supplemental screening with magnetic resonance imaging (MRI) has been recommended since 2007 for women at high risk for breast cancer beginning at age 25–308: a) in those with known or suspected pathogenic mutation in BRCA1 or BRCA2 or other less common disease-causing mutations; b) in those with a 20%–25% lifetime risk of breast cancer based on models that assess risk of mutations; and c) in women with a history of chest radiation therapy before age 30 and at least 8 years earlier. High-risk women have been shown to have more advanced disease at diagnosis and interval cancer rates as high as 50% with mammographic screening alone.9-11
Recommendations for annual supplemental screening with MRI (to begin by age 25–30 in such women) are independent of breast density and are based on many studies showing improved detection of early-stage breast cancer using MRI in high-risk women (with supplemental cancer detection rates after mammography averaging over 10 per 1000).12
Importantly, Warner et al. showed increased detection of node-negative invasive cancer and reduction in late-stage disease among women with known pathogenic BRCA mutations who were screened with MRI compared to those who were not screened with MRI.13 An analysis of large studies of MRI in 3 countries showed low rates of interval cancers of 10% or less even among high-risk women when screened with MRI in addition to mammography.14
Improved detection of early breast cancers with good prognosis has been shown with MRI even for average-risk women.15 An abbreviated or “fast” MRI using only a few of the standard sequences can be performed with comparable accuracy to the full diagnostic protocol16 and at much lower cost and may make use of MRI more accessible to women whose only risk factor is dense breasts. This is currently under investigation by the American College of Radiology Imaging Network (ACRIN).