Study: Breast density increases risk of subsequent breast cancer

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Screening mammography with breast tomosynthesis in a 57-year-old woman.
Image source: RadioGraphics

Women with dense breasts may be at higher risk of subsequent breast cancer after DCIS, especially in the contralateral breast, according to a study published online Oct. 7 in Cancer Epidemiology, Biomarkers & Prevention.

Laurel A. Habel, PhD, and colleagues from the division of research at the Kaiser Permanente Medical Care Program examined whether mammographic density can predict risk of second breast cancers among patients with ductal carcinoma in situ (DCIS), noting that few strong predictors of these subsequent cancers have been identified.

The researchers included 935 women (60 percent of the study cohort was older than 55 years at diagnosis of DCIS, and 75 percent were Caucasian) in their study that were diagnosed with DCIS and treated with breast-conserving surgery between 1990 and 1997 at Kaiser Permanente of Northern California.

Habel and colleagues reviewed medical records of each patient for subsequent breast cancers, both DCIS and invasive, and a mammographer blinded to subsequent cancer status evaluated mammograms at diagnosis for density. Habel and colleagues also calculated the risk of subsequent breast cancer events during follow-up.  

Of the 935 eligible DCIS patients, 18 percent of patients had a subsequent ipsilateral breast cancer, and 6 percent of patients had a new primary cancer in the contralateral breast after an average follow-up period of 103 months. Patients with the greatest total area of density (upper 20 percent of values) were at increased risk for invasive disease or DCIS in the ipsilateral or contralateral breast compared with those with the smallest area of density (bottom 20 percent).

“Our results provide additional supporting evidence for an increase in risk of second breast cancers among DCIS patients with mammographically dense breasts,” wrote the authors, adding that the association appears to be strongest and most consistent for risk of cancer in the contralateral breast.

Habel believes that the findings regarding mammographic density could be important for physicians when making treatment decisions for DCIS. “While it’s not a strong enough risk factor on its own, it may be possible to combine it with other factors to improve risk assessment and inform treatment decisions,” she stated.

However, consistent estimates of risk for specific density categories are needed before clinical utility can be established, the authors warned. “Because higher mammographic density predicts lower sensitivity and specificity of screening mammography, high breast density may have clinical relevance on the accuracy of follow-up mammography for DCIS patients as well.”