The density of a woman’s breast tissue is determined during a mammogram and is categorized into one of 4 categories:

1. A) Fatty
2. B) Scattered
3. C) Heterogeneously dense
4. D) Extremely dense

Breasts that are classified as either heterogeneously dense (category B) or extremely dense (category D), are considered “dense breasts.”

Dense breasts are normal and common.   About 40% of women over the age of 40 have dense breasts. Dense breasts have two implications to be aware of. They have an increased risk of developing breast cancer AND a higher chance that the cancer will be missed on a mammogram. The larger issue is one of “masking” cancers. Cancers can be masked or missed in dense tissue because both dense breast tissue and cancers appear as white or light grey on a mammogram. Trying to find cancer in a dense breasts is like trying to find a snowball in a blizzard.   With an additional screening test such as ultrasound or MRI after a mammogramm the chance of detecting the cancer will be higher than with only a mammogram.

In France and Austria, based on national screening guidelines, additional screening is automatically offered to women with dense breast tissue. In these countries, mammography is combined with ultrasound. Unfortunately, this is not yet standard everywhere.