Thank you for responding!
Dear mammogram asymmetry: It is not uncommon for there to be an abnormality or asymmetric density on a mammogram. In these cases, a person would be called back for a second mammogram or spot compression. Many times these abnormalities end up being tissue that could have folded over on itself and it smoothes out with compression. If the asymmetry persists, additional evaluation will be necessary to determine what it is.