Study: There's more to breast cancer risk than density

By Brian Casey, staff writer

May 19, 2015 -- Is the breast density notification movement missing the forest for the trees? A May 19 study in Annals of Internal Medicine suggests that breast density shouldn't be the only factor to consider when deciding which women should receive supplemental breast imaging tests in addition to mammography.

A research team led by Dr. Karla Kerlikowske, of the University of California, San Francisco, assessed the impact of six different strategies for determining which women should receive supplemental imaging to detect interval cancers, or malignant lesions that appear between rounds of mammography screening (Ann Intern Med, Vol. 162:10, pp. 673-681).

The strategies ranged from using only breast density to determine whether a woman would get follow-up studies to basing follow-up exams on a combination of breast density and other risk factors, such as age and risk according to the five-year risk model developed by the Breast Cancer Surveillance Consortium (BCSC).

To determine which of the six strategies would be most effective, the researchers calculated the interval cancer rate in a group of 365,000 women ages 40 to 74 who received 831,000 mammography exams. They then correlated the interval cancer rate with the density status, age, and BCSC risk score of the women. Interval cancer rates were considered high if they exceeded 1 case per 1,000 mammography exams.

The researchers also calculated how many discussions about supplemental imaging exams would be required with the women for each strategy, and used that information to create a ratio of the number of discussions required to detect each interval cancer. Presumably, the strategy with the lowest ratio would be the most efficient, resulting in the highest number of cancers detected with the lowest rate of follow-up.

Projected outcome of strategies for supplemental imaging discussion
Type of follow-up strategy Ratio of supplemental imaging discussion to interval cancers detected
1. All women with extremely dense or heterogeneously dense tissue 1,124
2. All women with extremely dense tissue 892
3. Women ages 50-74 with extremely dense breasts or women 70-74 with heterogeneously dense tissue 842
4. Women with BCSC risk ≥ 1.67% and extremely dense breasts or risk ≥ 2.50% and heterogeneously dense breasts 694
5. Women ages 40-74 with extremely dense breasts or 40-49 with heterogeneously dense breasts 1,132
6. Women with BCSC risk ≥ 1.67% and heterogeneously or extremely dense breasts 870

The authors wrote that strategy No. 4 offered the best balance of interval cancers detected and the number of discussions of supplemental imaging that would be required. Simply offering supplemental imaging to all women with high tissue density could be targeting some women who actually have low rates of interval cancer and advanced-stage disease.

"Use of combinations of breast cancer risk and BI-RADS density identified twice as many women with dense breasts and a high rate of interval cancer after a normal digital mammography result compared with combinations of age and breast density," the authors wrote. "Density information combined with breast cancer risk could be used to prioritize women who could benefit from breast imaging tests with better specificity than digital mammography, such as tomosynthesis."

Copyright © 2015

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