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A mammogram is an x ray of the breast to reveal internal structures and screen for or diagnose breast cancer .


Mammograms can detect tumors of the breast that are too small to feel. They also detect about 80% of ductal carcinomas-in-situ (DCIS) (abnormal cells in the lining of the milk ducts). DCIS usually cannot be detected with a breast self-exam or clinical breast exam. However, some cases of DCIS become invasive cancers. Mammography can also detect micro-calcifications (tiny calcium deposits that often indicate the presence of breast cancer ).

Screening mammograms

Some 33.5 million mammograms are performed annually in the United States. About 70% of these are screening mammograms in women with no symptoms of breast cancer. Since age is the major risk factor for breast cancer and since early detection is very important for the prognosis, annual or biennial mammograms are recommended for all women beginning at least by age 50. Any woman who is expected to live for at least three to five more years should continue to have regular mammograms. No-cost or low-cost mammograms are available for low-income American women who lack health insurance.

Women who inherit specific mutations or changes in the breast-cancer-susceptibility genes BRCA1 and BRCA2 are at very high risk of developing breast cancer. These women should have mammograms every 6 to 12 months, beginning at about age 25 to 35, or at least five years before the youngest age of breastcancer diagnosis in a family member.

Other risk factors that may indicate the need for earlier and/or more frequent mammograms include:

  • a family history of breast cancer, especially in a mother, sister, or daughter diagnosed before age 50
  • first menstruation before the age of 12 or menopause after age 55
  • childlessness or first child after age 30
  • lifelong physical inactivity l alcohol consumption
  • postmenopausal weight gain or obesity
  • hormone-replacement therapy for more than five years
  • dense breasts, particularly in older women, since these have less fatty tissue and many glands and ligaments in which cancer tends to develop
  • previous breast cancer
  • two or more breast biopsies for benign (noncancerous) conditions
  • breast changes found with a biopsy, such as atypical hyperplasia (a noncancerous condition in which the cells are abnormal and increased in number)
  • lobular carcinoma-in-situ (LCIS) (abnormal cells in the lobules or glands that produce milk)
  • prenatal exposure to diethylstilbestrol (DES), which was administered to pregnant women between 1940 and 1971
  • radiation treatment to the chest, particularly at a young age.

Death rates from breast cancer declined between 1990 and 2008, in part because of earlier detection due to the widespread use of screening mammograms in older women. Studies have indicated that mammogram

Percentage of U.S. women who reported having had a mammogram within the past 2 years, by selected characteristics, selected years 1987–2005
 1987 1990 1991 1993 1994 1998 1999 2000 2003 2005
*Estimates are considered unreliable. Data preceded by an asterisk have a relative statndard error (RSE) of 20–30 percent. Date not shown have an RSE greater than
30 percent.
source: National Health Interview Survey, National Center for Health Statistics, Centers for Disease Control and Prevention, U.S. Department
of Health and Human Services.
(Illustration by GGS Information Services. Cengage Learning, Gale)
Age groups Women age 40 and over
65 and over22.843.448.
75 and over17.335.837.841.044.657.258.961.360.654.7
Race and Hispanic origin Women age 65 and over
White, not Hispanic or Latino24.043.849.154.754.964.366.868.368.164.7
Black, not Hispanic or Latino14.139.741.656.361.060.668.165.565.460.5
Hispanic or Latino (of any race)*41.140.9*35.748.
Below 100 percent13.130.835.241.743.251.957.654.857.052.3
100–199 percent19.938.641.847.047.957.860.260.362.856.2
200 percent or more29.751.557.864.364.970.172.575.072.670.1
No high school
diploma or GED
High school diploma or GED25.947.554.057.459.166.868.471.869.764.3
Some college or more32.356.757.964.864.371.377.

screenings reduce the number of breast-cancer deaths in women aged 40 to 60, especially in women over 50. Medicare began reimbursing for screening mammograms in 1991 and breast-cancer deaths in women aged 65 and older declined. However, a 2006 study found that breast-cancer diagnosis was delayed in women aged 70 and older, in large part due to underutilization of screening mammography. A 2008 study found that insurance co-payments deterred many older women from having mammograms, although elderly white women were more likely to have mammograms than women in other racial and ethnic groups.

Diagnostic mammograms

Diagnostic mammograms are performed when the following is the case:

  • a lump or change in the breast is noticed during self-examination or an annual breast exam by a healthcare provider
  • a suspicious area is found with a screening mammogram
  • some breast tissue was obscured during a screening mammogram due to breast implants or other special circumstances.

With a diagnostic mammogram more x-ray pictures are taken from different angles and a suspicious area may be magnified. Diagnostic mammograms are used to determine the exact location of a lump and to look for other abnormalities in both breasts.


False positives

Most abnormal mammography results are not cancers. Because mammography is designed to be sensitive enough to detect very small, early-stage cancers, false-positive results are common. Abnormal results that require further testing occur with 5 to 15% of mammograms. Women in their 40s who get annual mammograms have about a 30% chance of a false-positive result during that decade. Women over age 50 have about a 25% chance of a false positive in a 10-year period. Questionable or false-positive results can cause anxiety and may require a biopsy (the removal of a small amount of cells or tissue from the breast).

False positive results are more common in the following cases:

  • younger women
  • women with a family history of breast cancer
  • women who have had breast biopsies
  • women who take estrogen as hormone-replacement therapy.

False negatives

Studies have suggested that about 10 to 20% of breast cancers detected by self-examination or a clinical breast exam are not detectable by mammography. Detecting breast cancer with a mammogram may depend on the following:

  • the size of the tumor
  • the rate of tumor growth
  • the density of the breast tissue
  • the level of female hormones such as estrogen and progesterone
  • the skill of the radiologist who examines the mammogram.

It can be difficult to discern tumors in dense breast tissue by mammography. Both false-positive and false-negative results are more common in younger women than in older women. False negatives are also common in older premenopausal (perimen-opausal) women with dense breasts. As women age their breasts often become less dense and develop more fatty tissue, making cancer easier to detect. Breast-tissue density also can be affected by estrogen-replacement therapy, menopause , and weight gain or loss. False-negative mammography results can cause a woman to delay seeking treatment for breast cancer even if she has symptoms.

Other precautions

The amount of radiation exposure from a mammogram is very small; however, if the breasts are large or dense higher doses of radiation are required to obtain a clear image. The allowable limit for each exposure of the breast is 0.3 rad (Radiation Absorbed Dose). Most mammograms deliver only a small fraction of that amount or about the amount that a person receives from background radiation in three months. Nevertheless exposure to radiation is a risk factor for breast cancer, particularly in younger women and at higher doses. It is generally considered that for women over age 40, the benefits of an annual screening mammogram outweigh the risk of radiation exposure.

For a woman who has a life expectancy of less than five years, screening for and detecting early breast cancer may lead to treatment that reduces her quality of life without extending survival. Some experts believe that screening mammograms for women over age 65 can lead to anxiety and further tests and that any detected breast cancers are usually not life-threatening. However, medical practitioners as of 2008 typically call for women over age 65 to continue to receive screening mammography. As more and more people over the age of 65 are active, healthy, and fit, many medical professionals want to encourage and not discourage regular recommended screening. In addition, although the cancer detected may not be life-threatening, some of those detected will be a threat to the woman's life and wellbeing. Early detection is still desirable.


Mammograms are x rays taken with a specially designed machine. Screening mammograms usually take two views of each breast—from above and angled from the side. Diagnostic mammograms generally take additional views and the procedure takes somewhat longer.

In the original mammogram test, the woman dresses in a loose-fitting gown that opens in the front. A registered radiologic technologist positions the woman beside the x-ray unit, lifts her breast, and compresses it between two flat plastic plates to hold it in place. The breast is flattened as much as possible. Spreading out the tissue makes it easier to see any abnormalities using the least possible radiation. Compressing the breast may cause discomfort or even pain for the few seconds required to take the x ray. The woman holds her breath and remains completely still for those few seconds. The x-ray film cassettes under the breasts are developed immediately to assure that the pictures are adequate. They are then examined by a radiologist.

Breasts with implants require a technologist experienced in their mammography technique because implants can hide some of the breast tissue. The technologist may gently lift the breast tissue away from the implant.

Full-field digital mammography (FFDM) is a subsequent method in which electronic images of the x rays are stored directly onto a computer. Possible advantages of FFDM over film mammography include:

  • increased sensitivity under some circumstances
  • the ability to send images electronically to other clinics or physicians for baseline comparisons, expert consultation, or second opinions
  • the ability to electronically enhance an image
  • a decrease in radiation exposure of about 25%

In a clinical trial of almost 50,000 women digital mammography was found to be superior to x-ray films for screening the following groups:

  • women under age 50, regardless of breast-tissue density
  • any woman with very dense breasts
  • pre- or peri-menopausal women, defined as those who had a last menstrual period in the previous 12 months.

Digital mammography had no advantages over x-ray film for women who were over 50, were not perimenopausal, and did not have dense breast tissue. Overall digital and x-ray-film mammography both detected about 70% of breast cancers. However, for women with dense breasts x-ray film detected only 55% of the cancers compared with 70% with digital mammography.

Computer-aided detection (CAD) searches for abnormalities in density, mass, and calcification in a digitized image from either a digital mammogram or an x-ray film. However, some research suggests that CAD may be less accurate than manual readings.


Preparations for a mammogram involve:

  • scheduling the procedure for about one week after the start of a menstrual period, when breasts are the least tender
  • mentioning any breast implants to the appointment clerk so that an experienced technologist is available
  • not using underarm deodorant, powders, lotion, or perfume on the day of the mammogram, since these products can interfere with the x rays and cause false positives or artifacts
  • wearing a shirt with shorts, pants, or a skirt to facilitate undressing from the waist up.


Usual activities can be resumed immediately after a mammogram.


Mammograms may detect some breast cancers that will never cause symptoms or become life-threatening. However, since it is not possible as of 2008 to determine which breast cancers will become invasive, all detected cancers are usually treated, possibly resulting in serious treatment-related side effects. If cancer detected by a mammogram is fastgrowing or has already spread to other parts of the body, treatment may not be beneficial.


  • How often should I have a screening mammogram?
  • What do my results mean?
  • Now that I am 65 should I continue to have regular mammograms?


Mammogram results are mailed to the patient within 30 days. Women can take their x-ray films with them or have them sent to another doctor or clinic.

The American College of Radiology has established a uniform system for mammogram results, the Breast Imaging Reporting and Database System (BI-RADS):

  • 0—unreadable; additional imaging needed for categorization
  • 1—negative; continue annual mammogram screenings for women over 40
  • 2—benign finding; continue annual mammogram screenings for women over 40
  • 3—probably benign; follow-up screening mammogram in six months
  • 4—suspicious abnormality; may require biopsy
  • 5—highly suggestive of malignancy (cancer); requires biopsy
  • 6—known biopsy-proven malignancy; biopsy to confirm cancer before beginning treatment.

If an abnormality is suspected from a mammogram, the patient may have magnetic resonance imaging (MRI), an ultrasound, or a biopsy. MRIs are more sensitive for identifying small cancers; however, they are even more likely than mammograms to produce false-positive results. An ultrasound can distinguish between a solid lump and a fluid-filled cyst. Cysts are usually not cancerous. If the lump is solid, a biopsy is performed to remove cells for examination.


Atypical hyperplasia —An increase in abnormal but noncancerous breast cells.

Biopsy —The removal of cells or tissue for examination by a pathologist.

BI-RADS —Breast Imaging Reporting and Database System; the American College of Radiology uniform system for reporting mammogram results.

BRCA1, BRCA2 —Breast-cancer susceptibility genes; specific mutations in these genes greatly increase the risk of breast cancer.

CAD —Computer-aided detection; software that searches digitized mammogram images for abnormalities.

Digital mammography —Full-field digital mammography, FFDM; electronic images of mammogram x rays that are stored directly on a computer rather than on film.

Ductal carcinoma-in-situ (DCIS) —Breast cancer that has not spread beyond the lining of the milk duct.

Lobular carcinoma-in-situ (LCIS) —Breast cancer that is confined to the lobules or milk-producing glands.

Microcalcification —Tiny abnormal deposits of calcium salts in the breast that often indicate breast cancer.

Caregiver concerns

The U.S. Food and Drug Administration certifies mammography facilities, including the technologist who takes the mammogram, the radiologist who interprets it, and the medical physicist who tests the equipment. Mammograms are performed in the following settings:

  • private radiology offices
  • mobile vans
  • breast clinics
  • hospital radiology departments.



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American Cancer Society, 1599 Clifton Rd. NE, Atlanta, GA, 30329, (404) 320-3333, (800) ACS-2345,

“Get a Mammogram: Do It for Yourself, Do It for Your Family” Campaign, National Cancer Institute, NCI Public Inquiries Office, 6116 Executive Blvd., Room 3036A, Bethesda, MD, 20892-8322, (800) 4-CANCER,

Susan G. Komen Breast Cancer Foundation, 5005 LBJ Freeway, Suite 250, Dallas, TX, 75244, (972) 855-1600, (877) GO-KOMEN,

Margaret Alic Ph.D.

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