. The most common cause of asymmetry during a screening mammogram is the superposition of normal breast tissue (summation artifact) breast cancer 5. Therefore, to understand the developing asymmetry, one. There are risks and benefits to mammograms but a new study shows women are ignoring the risks. Getting called back after a screening mammogram is pretty common but can be scary. 66. . Impression Asymmetric density in the right breast. 16 of screening and. . The most common cause of asymmetry during a screening mammogram is the superposition of normal breast tissue (summation artifact) breast cancer 5. . .