These two undated photos, provided by the American College of Radiology shows an extremely dense breast, left, and a least dense breast. Women whose breast tissue is very dense have a  greater risk of developing breast cancer than women whose breasts contain more fatty tissue. And it can be harder for mammograms to spot a possible tumor because both dense tissue and potentially cancerous spots appear white on the X-ray. This image compares mammograms of an extremely dense breast and an extremely fatty breast. According to the American College of Radiology, most women fall somewhere in between. (AP Photo/American College of Radiology)
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