Routine reporting of mammographic density from screening mammograms

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Mammographic density (MD) refers to the relative proportion of radiopaque fibroglandular tissue, versus radiolucent fat, on mammograms. MD can only be determined from mammograms. The population distribution of MD by the Breast Imaging‐Reporting and Data System category is: (a) almost entirely fatty – 10%; (b) scattered areas of fibroglandular density – 40%; (c) heterogeneously dense – 40%; and (d) extremely dense – 10%.1
High MD is an independent, strong, common and modifiable risk factor for breast cancer. Women with extremely dense breasts have 4.75 times higher risk of breast cancer than women with fatty breasts.2 Women with above‐average MD have 1.2–2 times higher risk of breast cancer than those in group (b). High MD masks cancers, decreasing the accuracy of mammography.3
MD is the most common method for measuring breast density. Its significance is modified by age and body mass index. Twin studies show that genetic factors determine 60–70% of MD.4 MD declines with age and increases with hormone replacement therapy use,5 and with increasing body mass index.6
In the USA, legislation in most states requires radiology providers to notify women of their MD, explain the impact of MD on cancer detection and provide suggestions for supplemental screening.

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