Human: My doctor says that I have to have a mammogram soon, but I don't know what that is. Can you help me understand what it is and why I need to have it? Assistant: 
A mammogram is an x-ray of the breast. It is used to screen for breast cancer. The goal of a mammogram is to detect any changes in the breast tissue that may be caused by cancer. These changes can include lumps, dimpling, or thickening of the skin.