Mammography is an X-ray test of the breasts (mammary glands) that is used to diagnose breast cancer. The resulting X-ray picture is called a mammogram.

X-rays are a form of radiation, like light or radio waves that can be focused into a beam, much like a flashlight beam. Unlike a beam of light, however, X-rays can pass through most objects, including the human body. When X-rays hit a piece of photographic film, they can produce a picture. Dense tissues in the body, such as bones, block (absorb) many of the X-rays and show white on an X-ray picture. Less dense tissues, such as muscles and organs, block fewer of the X-rays (so more of the X-rays pass through) and show in shades of gray. X-rays that pass only through air show black.

A mammogram is done to help screen for or diagnose breast cancer. Many small tumors can be seen on a mammogram before they can be felt by a woman or her doctor. Cancer revealed on an early stage is more easily treated and cured.

Although breast cancer can occur in men, 99% of all breast cancer is found in women. Factors that affect a woman's risk for breast cancer include:

• Age. The risk of breast cancer increases gradually as women age. Breast cancer is uncommon in women under the age of 35. All women age 40 and older are at risk for breast cancer. However, most breast cancers occur in women over the age of 50, and the risk is especially high for women over age 60.
• Family medical history. Having a mother or sister (or both) who had breast cancer, increases a woman's risk of developing breast cancer. If a woman's family member developed breast cancer before menopause, her risk is about 3 to 4 times greater than another woman of the same age who does not have a family history of breast cancer. If the family member developed breast cancer after menopause, the risk is about twice as great.
• Genetic alterations. Changes in certain genes (BRCA-1, BRCA-2, and others) make women more susceptible to breast cancer. In families in which many women have had the disease, genetic testing can show whether a woman has specific genetic changes known to increase her susceptibility to breast cancer. Doctors may suggest ways to reduce the risk of breast cancer or to improve the detection of breast cancer in women who have the genetic alterations. Early mammography may be recommended for women who carry BRCA-1 or BRCA-2 gene mutations.
• Late childbearing. Women who had their first child after the age of 30 have a greater chance of developing breast cancer than women who had their children at a younger age.
• Age when menstruation began. Starting menstrual periods before the age of 12 slightly increases the risk of breast cancer.
• Age at menopause. Going through menopause after the age of 55 slightly increases the risk of developing breast cancer.
• Radiation exposure. Women whose breasts were exposed to significant amounts of radiation at a young age (especially those who were treated with radiation for childhood Hodgkin's disease or thyroid disease) have an increased risk for developing breast cancer. However, the amount of radiation received from a diagnostic chest X-ray during childhood is not significant and does not increase the risk for developing breast cancer.
• Previous breast biopsies. Having had at least two breast biopsies done for a noncancerous (benign) breast disease, especially for atypical hyperplasia, increases the risk of developing breast cancer.
• Hormone replacement therapy. Taking hormone replacement medication after menopause for longer than 5 years slightly increases the risk of developing breast cancer.

However, most women who develop breast cancer do not have significant risk factors for the disease; for example, only 5% to 10% of breast cancers are familial. No one can predict who will develop breast cancer.

All organizations that produce guidelines about mammograms recommend regular mammograms (every 1 to 2 years) for women over the age of 50. Most of these organizations recommend yearly mammograms.

If you do not have any risk factors for breast cancer, consider these medical facts when deciding about having mammograms between the ages of 40 and 50:

• All women age 40 and older are at risk for breast cancer. However, most breast cancers occur in women older than 50, and the risk is especially high for women older than 60.
• Yearly mammograms have been shown to prevent some deaths from breast cancer. 
• Mammograms do not prevent breast cancer or reduce a woman's risk of developing cancer. Regular mammograms can reduce a woman's risk of dying from breast cancer by detecting a tumor when it is more easily treated.

Many organizations (such as the American Cancer Society and the American College of Radiologists) recommend mammograms every year for women between the ages of 40 and 49. Others, such as the National Cancer Institute, recommend mammograms every 1 to 2 years. Women in this age group should discuss the medical evidence concerning mammograms with their doctors when deciding how often to have a mammogram.

About 10% of breast cancers can be felt as a breast lump, but do not show up on mammography. For this reason, doctors recommend that mammography be combined with clinical breast exams done by a health professional.

Even if a mammogram is normal, examining a sample (biopsy) of a suspicious breast lump under a microscope may be needed. 

Mammography
Results

Mammography results are usually available within 10 days. It is not uncommon to be asked to return for another test so an additional view of an area in question can be obtained.

In the United States, all facilities that perform mammography must send a copy of the test results (written in language that is easily understood) within 30 days directly to the woman who had the test.

Abnormal mammogram results require additional tests (such as a biopsy) to determine if cancer is present. However, most abnormalities found during mammography are not cancer.