I just had a mammogram, and the hospital has asked me to come in for extra images on my left breast, because they have found an area of dense breast tissue that they are not sure about. This is my second mammogram, and my baseline mammogram from 7 years ago apparently does not have this tissue. Can only one breast be normally dense, or is this a sign of abnormality? I am 42 years old, my paternal grandmother had breast cancer and lost her left breast at about 35 years old. I am basically very healthy and work out a lot, eat well most of the time and don't drink too much or smoke.