Breast Ultrasound Added to Mammography Increases Cancer Detection

More breast cancer lesions were diagnosed in women with dense breasts when ultrasound screening was conducted in conjunction with mammography compared with mammography alone, according to a study presented at the San Antonio Breast Cancer Symposium (SABCS) 2014.¹

“We found that among women with dense breasts, screening breast ultrasonography detected a significant number of breast cancers not discovered by mammography,” Jean M. Weigert, MD, of the Hospital of Central Connecticut, New Britain, explained.

According to the Radiological Society of North America, mammography is considered the best single modality for population-based screening, but its sensitivity is diminished by up to 20% in patients with dense breasts, due in most part to masking, a phenomenon in which surrounding dense breast tissue obscures a cancer on mammography.²

Four years of ultrasound data from 2 sites (5 offices) in Connecticut were included in the analysis presented at SABCS. A retrospective analysis of data from these sites was conducted from 2009 to 2013 by Weigert and colleagues. Approximately 30,000 screening mammograms were included for each year in patients ranging in age from 45 to 77 years.

A total of 46 cancers or high-risk lesions not visible on screening mammography were identified by ultrasound, ranging in size from 0.3 to 8.0 centimeters. These lesions were not palpable, and most patients did not have additional risk factors other than dense breasts. Four patients had positive metastatic lymph nodes.

The number of breast ultrasounds conducted for dense breasts was 2706 in year 1, 3351 in year 2, 4128 in year 3, and 3331 in year 4. Ultrasonography detected between 11 and 13 breast cancers per year during this 4-year period, representing between 3 and 4 breast cancers per 1000 women screened. During years 3 and 4, cancers were found in patients who had a prior ultrasound screening, although their mammograms remained negative. These cancers were small and node negative.

The positive predictive value (the proportion of women with breast cancer among those with a positive breast ultrasound result) improved over the 4-year period. In year 1, the positive predictive value was 7.1%; in year 4, it was 17.2%.

“The positive predictive value for mammography is about 20% to 30%, and we are getting close to that with breast ultrasonography now that we are more experienced,” Weigert said. “Without the additional screening, we do not know at what point these lesions diagnosed with screening breast ultrasonography would have been clinically evident, either on mammography or physical examination. Of concern, the number of eligible women who elect to undergo the additional test remains low, at about 30%, which is due to several factors, including education and cost.”

Beginning in 2009, legislation mandated that patients undergoing mammography in Connecticut be informed that further screening may be of benefit if they have dense breasts.

In California, which enacted mandatory reporting in 2013, the law requires that patients with dense breast tissue on screening mammography receive notification in writing, with advice on discussing their screening options with their primary physician. Approximately 50% of women undergoing screening mammography are classified as having either “heterogeneously dense” or “extremely dense” breasts. In California alone, this could mean 2 million notification letters a year, and a significant increase in supplementary screening with magnetic resonance imaging and ultrasound.

According to Jafi A. Lipson, MD, of the California Breast Density Information Group (CBDIG), while studies do show that additional cancers are found with supplementary screening breast ultrasound, “this is at the price of a large number of benign breast biopsies.”²

Clinical Pearls

• More breast cancer lesions were diagnosed in women with dense breasts when ultrasound screening was conducted in conjunction with mammography compared with mammography alone.
• Retrospective analysis included 4 years of ultrasound data and approximately 30,000 screening mammograms per year from 2 sites in Connecticut.
• A total of 46 cancers or high-risk lesions not visible on screening mammography were identified by ultrasound; the lesions were not palpable, and most patients did not have additional risk factors other than dense breasts.
• The positive predictive value of breast ultrasound improved over the study period (7.1% and 17.2% in years 1 and 4, respectively).

He added that “supplemental screening of the approximately 40 percent of California women with heterogeneously dense breasts would result in very substantial additional cost to the healthcare system. There also is concern that the increased use of supplementary screening will ultimately expose some patients to more harm, in the form of false-positive results, than good.”²

The CBDIG offers a website designed to provide information about breast density, breast cancer risk assessment, and supplementary imaging.^3,4

A recent study on the prevalence of mammographically dense breasts in the United States5 indicated that more than 25 million women who would typically undergo breast screening fall into this category. The authors, led by Brian L. Sprague, PhD, with the University of Vermont, Burlington, recommend that “policymakers and healthcare providers should consider this large prevalence when debating breast density notification legislation and designing strategies to ensure that women who are notified have opportunities to evaluate breast cancer risk and discuss and pursue supplemental screening options if deemed appropriate.”

References

1. Weigert JM. The Connecticut experiment: 4 years of screening women with dense breasts with bilateral ultrasound. Presented at: 2014 San Antonio Breast Cancer Symposium; December 9-13, 2014; San Antonio, Texas. Abstract [S5-01].
2. Experts take on challenge of breast density notification laws [news release]. Oakbrook, IL: Radiologic Society of North America. http://www2.rsna.org/timssnet/media/pressreleases/pr_target.cfm?ID=691. Accessed December 16, 2014.
3. California Breast Density Information Group. Frequently asked questions about breast density, breast cancer risk, and the breast density notification law in California: a consensus document. www.breastdensity.info. Accessed December 16, 2014.
4. Price ER, Hargreaves J, Lipson JA, et al. The California breast density information group: a collaborative response to the issues of breast density, breast cancer risk, and breast density notification legislation.Radiology. 2013;269(3):887-892.
5. Sprague BL, Gangnon RE, Burt V, et al. Prevalence of mammographically dense breasts in the United States.J Natl Cancer Inst. 2014;106(10).

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