Not All Women With Dense Breasts Need Extra Imaging

Beth Skwarecki

May 18, 2015

Women with dense breasts are not necessarily at higher risk for cancer in the year after a normal mammogram, according to a prospective cohort study on breast cancer risk. Investigators calculated that risk is elevated only for the 24% of women with extremely or heterogeneously dense breasts who also have other risk factors.

"Breast density should not be the sole criterion for deciding whether supplemental imaging is justified because not all women with dense breasts have high interval cancer rates," write Karla Kerlikowske, MD, from the General Internal Medicine Section at the San Francisco Veterans Affairs Medical Center in California, and colleagues in an article published online May 18 in the Annals of Internal Medicine.

The researchers note that interval cancers, defined as those that are diagnosed within a year after a normal mammogram, are more aggressive and that women at high risk for these cancers are likely to benefit the most from supplemental imaging. However, it is not yet clear whether all women with dense breasts are at high risk for interval cancers.

To find out, investigators analyzed digital screening mammograms from 365,426 women aged 40 to 74 years during a period of 9 years (for a total of 831,455 mammograms). The data came from the Breast Cancer Surveillance Consortium's mammography registries. They excluded first mammograms and unilateral mammograms, and those less than 9 months apart were excluded.

To determine other risk factors, the investigators used the Breast Cancer Surveillance Consortium's 5-year risk model, which considers age, first-degree relatives with breast cancer, biopsy history, and race or ethnicity in addition to breast density as categorized by the Breast Imaging Reporting and Data System (BI-RADS density). A 5-year risk between 1.00% and 1.66% is considered "average," and a risk above 2.50% is considered "high."

The investigators found interval cancer rates greater than 1 case per 1000 mammograms in women with extremely dense breasts if they had a 5-year risk of 1.67% or greater (47.5% of women with extremely dense breasts) and in women with heterogeneously dense breasts and a 5-year risk of 2.5% or greater (19.5% of women with heterogeneously dense breasts). Together, these women made up 24% of those with dense breasts and 12% of the total population screened.

For the remaining 51% of women with dense breasts and 52.5% of those with extremely dense breasts the 5-year risk was low to average (1.66% or less).

The investigators suggest that providers use the Breast Cancer Surveillance Consortium 5-year risk calculator to discuss additional imaging with patients who have dense breasts. They note that a limitation of the study was that they did not specifically assess the benefits of additional screening.

The study "provides compelling evidence that breast density should not be the sole criterion to guide decisions about supplemental breast cancer screening," write Nancy Dolan, MD, and Mita Sanghavi Goel, MD, from the Northwestern University Feinberg School of Medicine in Chicago, Illinois, in an accompanying editorial. "This finding suggests that federal legislation on management of screening in women with dense breasts is premature." Twenty-two states have laws requiring women to be notified if mammograms reveal that they have dense breast tissue, and federal legislation has been introduced in Congress.

"Given the lack of scientific consensus, resources targeted for breast density legislation would be better devoted toward more accurate identification of women at high risk for interval breast cancer, research on optimal use of imaging methods, reduction of disparities in screening and early detection, and training of front-line primary care providers on breast cancer risk assessment," they write.

Ann Intern Med. Published online May 28, 2015.

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