Human: My doctor says I have to have a mammogram. What is a mammogram and why is it so important? Assistant: 
A mammogram is an x-ray of the breast used to detect early signs of cancer. It is recommended that women over 40 should get screened for breast cancer every two years, and those who are at higher risk should get screened annually. A mammogram can help doctors diagnose breast cancer in its earliest stages when it is most treatable.