What is a Mammogram?

A mammogram is an x-ray picture of the breast. Mammograms can be used to check for breast cancer in women who have no signs or symptoms of the disease. This type of mammogram is called a screening mammogram. Screening mammograms usually involve two or more x-ray pictures, or images, of each breast. The x-ray images often make it possible to detect tumors that cannot be felt.

Screening mammograms can also find microcalcifications (tiny deposits of calcium) that sometimes indicate the presence of breast cancer.

Mammograms can also be used to check for breast cancer after a lump or other sign or symptom of the disease has been found. This type of mammogram is called a diagnostic mammogram. Besides a lump, signs of breast cancer can include breast pain, thickening of the skin of the breast, nipple discharge, or a change in breast size or shape; however, these signs may also be signs of benign conditions. A diagnostic mammogram can also be used to evaluate changes found during a screening mammogram or to view breast tissue when it is difficult to obtain a screening mammogram because of special circumstances, such as the presence of breast implants.

How are screening and diagnostic mammograms different?

The same machines are used for both types of mammograms. However, diagnostic mammography takes longer to perform than screening mammography and the total dose of radiation is higher because more x-ray images are needed to obtain views of the breast from several angles. The technologist may magnify a suspicious area to produce a detailed picture that can help the doctor make an accurate diagnosis.

What are the benefits and potential harms of screening mammograms?

Early detection of breast cancer with screening mammography means that treatment can be started earlier in the course of the disease, possibly before it has spread. Results from randomized clinical trials and other studies show that screening mammography can help reduce the number of deaths from breast cancer among women ages 40 to 74, especially for those over age 50. However, studies to date have not shown a benefit from regular screening mammography in women under age 40 or from baseline screening mammograms (mammograms used for comparison) taken before age 40.