Breast Density should not be the Sole Criterion in Determining High Risk for Breast Cancer

Research by Kerlikowske et al published in the Annals of Internal Medicine suggests that not all women with dense breasts are at high enough risk for breast cancer after a normal mammogram to justify having more diagnostic tests such as ultrasound or MRI.

The researchers used data from Breast Cancer Surveillance Consortium (BCSC) breast imaging facilities.

Studies of 365 426 women aged 40 to 74 years who had 831 455 digital screening mammographic examinations were reviewed.

BI-RADS breast density, BCSC 5-year breast cancer risk, and interval cancer rate (invasive cancer ≤12 months after a normal mammography result) per 1000 mammography examinations. High interval cancer rate was defined as more than 1 case per 1000 examinations.

High interval cancer rates were observed for women with 5-year risk of 1.67% or greater and extremely dense breasts or 5-year risk of 2.50% or greater and heterogeneously dense breasts (24% of all women with dense breasts). The interval rate of advanced-stage disease was highest (>0.4 case per 1000 examinations) among women with 5-year risk of 2.50% or greater and heterogeneously or extremely dense breasts (21% of all women with dense breasts). Five-year risk was low to average (0% to 1.66%) for 51.0% of women with heterogeneously dense breasts and 52.5% with extremely dense breasts, with interval cancer rates of 0.58 to 0.63 and 0.72 to 0.89 case per 1000 examinations, respectively.

In this study half of women had mammograms that showed dense breasts. For most women who had a mammogram, the risk for breast cancer after a normal mammogram was low, even for those who had dense breasts and low 5-year breast cancer risk. Two groups of women had the highest risk for breast cancer after a normal mammogram: those with extremely dense breasts and an intermediate or high 5-year cancer risk, and those who had different patterns of breast density and a high or very high 5-year cancer risk.

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. BCSC 5-year risk combined with BI-RADS breast density can identify women at high risk for interval cancer.