Mammograms with different breast densities.
Four mammograms with different breast density categories are shown. Breasts can be almost entirely fatty (see A), or have scattered areas of dense fibroglandular breast tissue (see B). Dense breasts are either heterogeneously dense and have many areas of glandular and connective tissue (see C), or are extremely dense (see D).
Having dense breasts is a risk factor for two reasons. Mammography is less effective and early signs of cancer are obscured by the dense tissue. In addition, but independently, patients with dense breasts are more likely to develop breast cancer.
Image courtesy of https://densebreast-info.org