I can see clearly now.

Top Line: Dense breasts have a higher proportion of opaque parenchymal tissue on mammogram, making abnormalities such as cancer more difficult to visualize, and the additional parenchyma is also associated with an increased risk of breast cancer.

The Study: What is dense breast tissue, anyway? BI-RADS has a 4-point scale where “C” is heterogeneously dense, and “D” is extremely dense to the point that it obscures mammography sensitivity. It’s this latter category that may benefit from supplemental screening such as breast MRI. The DENSE trial included over 40K women ages 50-75 in the Dutch mammography screening program who had extremely dense breast tissue. They were randomized 1:4 to have a supplemental MRI or routine screening, though just over half randomized to MRI actually had the MRI. The incremental cancer detection rate with supplemental MRI was 16.5 per 1000 screenings, while the false positive rate was 8%, or 80 per 1000 screening. Put another way, among the women who had a biopsy after MRI, only a quarter actually had cancer. But in the interval between the subsequent mammography 2 years later, supplemental MRI screening significantly lowered the risk of subsequent breast cancer diagnosis from 5.0 → 2.5 cancers per 1000 screenings. Now, this is the initial report after the initial round of biennial screening, and mostly small breast cancers were detected. It remains to be seen whether this strategy can reduce the rate of more advanced breast cancer.

TBL: Supplemental breast MRI after negative mammogram for women with extremely dense breasts halves the rate of breast cancer that develops in the interval between biennial mammography. | Bakker, N Engl J Med 2019