A screening mammogram is an x-ray exam of the breast on a woman who has no symptoms. The goal of a screening mammogram is to find cancer when it is still too small to be felt by a woman or her doctor. Finding small breast cancers early with a screening mammogram greatly improves a woman's chance for successful treatment.

A screening mammogram usually takes 2 x-ray pictures (views) of each breast. Some patients, such as those with large breasts, may need to have more pictures to see as much breast tissue as possible.

How is a mammogram done?

When you have a mammogram, your breast is compressed or squeezed between 2 plates attached to the mammogram machine -- a plastic plate (on top) and an x-ray plate (on the bottom). The technologist compresses your breast to keep it from moving, and to make the layer of breast tissue thinner. These measures reduce the x-ray exposure, reduce blurring, and make the picture sharper. Although the compression can feel uncomfortable and even painful for some women, it only lasts for a few seconds and is needed to get a good picture. The entire procedure for a mammogram takes about 20 minutes.

The x-ray device and compression plates used for mammograms

Mammograms produce a black and white x-ray picture of the breast tissue. Depending on the type of machine, the picture is either on a large sheet of x-ray film or is an electronic image that can be seen on a computer screen. Today, more than half of the mammography units used are screen-film units, which means they produce the mammogram picture on x-ray film. The other half are newer full-field digital mammography units, which capture the picture in digital format that can be looked at on a computer screen.

No matter what kind of x-ray image is taken -- film or electronic -- it is interpreted (or "read") by a doctor, most often a radiologist. Radiologists are doctors who have special training in diagnosing diseases by looking at pictures of the inside of the body produced by x-rays, sound waves, magnetic fields, or other methods. Other doctors who treat breast diseases may look at the mammogram, too.

Reading mammograms is challenging. The way the breast looks on a mammogram varies a great deal from woman to woman. And some breast cancers may cause changes in the mammogram that are hard to notice. If you have had mammograms in the past, it is very important that the radiologist has the x-ray films or digital pictures so they can be compared with the new ones (not just the report). Comparing the pictures helps the doctor find small changes and detect a cancer as early as possible. Because it can be hard to get your older pictures, it is best to find a facility that you are comfortable with and plan to get your regular mammograms there each year. That way, your other pictures will be there and easy to find.

American Cancer Society recommendations for early breast cancer detection

Women age 40 and older should have a screening mammogram every year, and should continue to do so for as long as they are in good health.

Current evidence supporting mammograms is even stronger than in the past. Recent evidence has confirmed that mammograms offer substantial benefit for women starting in their 40s. Women can feel confident about the benefits associated with regular mammograms for finding cancer early.

But mammograms do have some have limitations. Although mammograms will detect most breast cancers, some will be missed. Also, sometimes signs on a mammogram that look abnormal may require a biopsy (the removal of a sample of tissue to see whether cancer cells are present) that will turn out not to be breast cancer. In this instance, a woman has undergone a procedure for an abnormality that wasn't cancer, and she has been through a period of feeling anxious about the possibility of having breast cancer. New research suggests a small percentage of breast cancers, especially a pre-cancerous condition called ductal carcinoma in situ, may not ever become life threatening, so treatment of these cancers is not necessary. (This is referred to as "overdiagnosis.") But mammograms, despite their limitations, are the most effective and valuable tool for decreasing suffering and death from breast cancer. Women should be told about the benefits, limitations, and potential harms linked with regular screening.

There is no fixed age at which women should stop getting mammograms. Mammograms for older women should be based on the woman's health and whether or not she has other serious illnesses. Age alone should not be the reason to stop having regular mammograms. As long as a woman is in good health and would be a candidate for treatment if she developed breast cancer, she should continue to have screening mammograms.

Women in their 20s and 30s should have a clinical breast exam (CBE) as part of a periodic (regular) health exam by a health professional, preferably every 3 years. After age 40, women should have a breast exam by a health professional every year.

CBE gives a better picture of breast problems than that offered by mammograms alone. It offers a chance for women to discuss breast changes with their doctors, physician assistants, or nurses. They can also talk about the importance of early detection and factors in the woman's history that might make her more likely to have breast cancer.

There may be some benefit in having the CBE shortly before the mammogram, because if the examiner detects an abnormality the mammogram can be done in such a way to pay closer attention to that area of the breast. The exam should include teaching and feedback so you will get more familiar with your own breasts. Women should also be given information about the benefits and limitations of CBE and breast self-exam (BSE). Breast cancer risk is very low for women in their 20s and slowly increases with age. Women should be told to report any new breast symptoms to a health professional right away.

Like mammography, the person doing a CBE will not find all breast cancers, and some masses that are felt will lead to a referral for biopsy and will be found not to be breast cancer.

Breast self-exam (BSE) is an option for women starting in their 20s. Women should be told about the benefits and limitations of BSE. Women should report any breast changes to a health professional right away.

Research has shown that BSE plays a small role in finding breast cancer compared with finding a breast lump by chance by a woman who knows what is normal for her. Some women feel very comfortable doing BSE (which is a systematic, step-by-step approach to looking at and feeling one's breasts) regularly, usually monthly. Other women are more comfortable simply looking and feeling their breasts in a less systematic approach, such as while showering or getting dressed, or doing an occasional thorough exam. Sometimes, women are so concerned about "doing it right" that they become stressed over the technique. Doing BSE regularly is one way for women to know how their breasts normally look and feel and to notice any changes. The goal, with or without BSE, is to find and report any breast changes to a doctor or nurse right away.

Women who choose to do BSE should have their BSE technique reviewed during their physical exam by a health professional. It is OK for women to choose not to do BSE or not to do it on a regular schedule. But by doing the exam regularly, you get to know how your breasts normally look and feel and you can more readily detect a change that occurs, such as development of a lump or swelling, skin irritation or dimpling, nipple pain or retraction (turning inward), redness or scaliness of the nipple or breast skin, or a discharge other than breast milk. Should you notice any changes you should see a health professional as soon as you can. But remember that most of the time these breast changes are not cancer.

As with mammography and CBE, women with BSE will not always find a breast cancer during self-exam. They also may feel a lump which could lead to a biopsy that is found to not be cancer.

Women at high risk of breast cancer (about 20% or greater lifetime risk based on a detailed family history or a history of radiation treatments at a young age), should get an MRI (magnetic resonance imaging) and a mammogram every year beginning at age 30 (see below). Women at moderately increased risk (15% to 20% lifetime risk) should talk with their doctors about the benefits and limitations of adding MRI screening to their yearly mammogram. Yearly MRI screening is not recommended for women whose lifetime risk of breast cancer is less than 15%.

Women at high risk include those who:

• Have a known BRCA1 or BRCA2 gene mutation
• Have a first-degree relative (mother, father, brother, sister, or child) with a BRCA1 or BRCA2 gene mutation, and have not had genetic testing themselves
• Have a lifetime risk of breast cancer of about 20% to 25% or greater, according to risk assessment tools that are based mainly on a family history that includes both her mother's and father's side
• Had radiation therapy to the chest when they were between the ages of 10 and 30 years
• Have a genetic disease such as Li-Fraumeni syndrome, Cowden syndrome, or hereditary diffuse gastric cancer, or have a first-degree relative with one of these syndromes

Women at moderately increased risk include those who:

• Have a lifetime risk of breast cancer of 15% to 20%, according to risk assessment tools that are based mainly on family history (see below)
• Have had breast cancer, ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), atypical ductal hyperplasia (ADH), or atypical lobular hyperplasia (ALH)
• Have extremely dense breasts or unevenly dense breasts when viewed by mammograms

If MRI is used, it should be in addition to, not instead of, a screening mammogram. This is because while an MRI is more likely to detect cancer than a mammogram, it may still miss some cancers that a mammogram would detect.

For most women at high risk, screening with MRI and mammograms should begin at age 30 years and continue for as long as a woman is in good health. But because the evidence is limited regarding the best age at which to start screening, some organizations recommend an earlier age. The decision about when to begin screening should be based on shared decision making between patients and their health care providers, taking into account personal circumstances and preferences.

Several risk assessment tools, with names such as the Gail model, the Claus model, BRACAPRO, BOADICEA, and the Tyrer-Cuzick model, are available to help health professionals estimate a woman's breast cancer risk. These tools give approximate, rather than precise, estimates of breast cancer risk based on different combinations of risk factors and different data sets. As a result, the different tools may give different risk estimates for the same woman. For example, the Gail model bases its risk estimates on certain personal risk factors, such as age at menarche and history of prior breast biopsies, along with any history of breast cancer in a woman's first-degree relatives on her mother's side. (So, the Gail model is not useful for determining if a woman may have inherited a mutation on a breast cancer susceptibility gene.) The Claus model estimates risk based on family history of breast cancer in both first and second-degree relatives. These 2 models could easily give different estimates for the same person. Results obtained from any of the risk assessment tools should be discussed by a woman and her doctor when being used to decide whether to start MRI screening.

Women who get screening MRI should do so only at a facility that can do an MRI-guided breast biopsy at the same time if needed. Otherwise, the woman with positive findings will have to have a second MRI exam at another facility where a biopsy can be done.

There is no evidence at this time that MRI will be an effective screening tool for women at average risk. While MRI is more sensitive than mammograms in very high-risk women, it also has a higher false positive rate (where the test finds things that turn out to not be cancer). This would lead to unneeded biopsies and other tests in many of these women.

The American Cancer Society believes the use of regular mammograms, MRI (in women at high risk), clinical breast exams, and finding and reporting breast changes early, according to the recommendations outlined above, offers women the best chance for detecting breast cancer at an early, more favorable stage. This combined approach is clearly better than any one test. Without question, breast physical exam without mammograms would miss many breast cancers that are too small for a woman or her doctor to feel but can be seen on mammograms. Although a mammogram is a sensitive screening method, a small percentage of breast cancers do not show up on mammograms but can still be felt by a woman or her doctor. For women at high risk of breast cancer, such as those with BRCA gene mutations or a strong family history, both MRI and mammogram exams of the breast are recommended.