Mammographic breast density affects breast cancer screening and women increasingly ask their general practitioners for advice.
Breast density refers to the relative amount of radio opaque stromal and glandular tissue compared to the amount of radiolucent breast fat demonstrated at mammography.
High breast density reduces the sensitivity of mammography because of its masking effect for cancer detection. Sensitivity may exceed 85% in fatty breasts and decreased to 65% in very dense breasts.
High breast density increases the risk of breast cancer. The relative risk for cancer in women with extremely dense breasts compared with average woman is approximately 2:1. Approximately 30-40% of women over the age of 50 have mammographically heterogeneously dense or extremely dense breasts.
Factors that influence breast density
Breast density as a risk factor for breast cancer relates to the amount of the breast’s glandular and stromal elements. As breast cancer most commonly arises in glandular cells a greater amount of glandular tissue increases the chance of cancer.
International evidence based review studies indicate there is considerable variation in the subjective classification of breast density by radiologists.
A woman’s breast density tends to vary with time due to menopausal changes, hormone replacement therapy and weight gain or loss.
The relative risk for breast density is much smaller than other major risk factors for breast cancer such as age, family history, reproductive history and genetic mutations
Is supplementary screening of benefit?
There are no randomised controlled trails evaluating the use of supplemental screening with whole breast ultrasound in women with dense breasts. Trials consistently demonstrated that supplementary breast ultrasound in women with dense breasts does increase cancer detection by 50% at the cost of a very high false positive biopsy rate.
The value of tomosynthesis, (3D mammography) as a supplemental screening modality in women with dense breasts is not yet proven. No studies have evaluated the benefits of adjunctive screening breast MRI in women of average risk with dense breasts.
Supplemental screening of women with dense breast who are average or low risk is not currently recommended by international evidence based review studies.
The American College of Radiologists/Society of Breast Imaging appropriateness criteria state that in women at intermediate risk of breast cancer due to a family history, a personal history of breast cancer, or other risk factors including premalignant lesions such as lobular neoplasia may benefit from regular supplemental whole breast ultrasound.