A mammography is a process when an x-ray of the breast is taken to detect and diagnose breast disease.

A mammogram can pick up very small tumours, even before they can be detected as a lump. It is used to screen for breast cancer, as well as to diagnose breast cancer. A diagnostic mammogram is used to diagnose breast disease in women who have breast symptoms. Screening mammography is used to look for breast disease in women who are asymptomatic; that is, they appear to have no breast problems.

Mammograms don’t prevent breast cancer, but they can save lives by finding breast cancer as early as possible. Finding breast cancers early with mammography also means that many more women being treated for breast cancer are able to keep their breasts. When caught early, localized cancers can be removed without resorting to breast removal (mastectomy).


It is recommended that women get a mammogram once a year, beginning at age 40. If you’re at high risk for breast cancer, with a strong family history of breast or ovarian cancer, or have had radiation treatment to the chest in the past, it’s recommended that you start having annual mammograms earlier – which you should discuss with your doctor.

Although breast x-rays have been performed for more than 70 years, modern mammography has only existed since 1969. That was the first year x-ray units dedicated to breast imaging were available. With modern mammography equipment used specifically for breast x-rays, very low levels of radiation are used, usually about 0.1 to 0.2 rad dose per x-ray.

Strict guidelines are in place to ensure that mammography equipment is safe and use the lowest dose of radiation possible. Many people are concerned about the exposure to x-rays, but the level of radiation in modern mammograms does not significantly increase the risk for breast cancer.


For a mammogram, the breast is compressed between 2 plates to flatten and spread the tissue. Although this may be uncomfortable for a moment, it is necessary to produce a good, “readable” mammogram. The compression only lasts a few seconds, and the entire procedure for screening mammography takes about 20 minutes.

Most standard mammogram includes two views of each breast taken from different angles. Even if you have a lump in only one breast, pictures will be taken of both breasts. This is so the breasts can be compared, and so that the other breast can be checked for abnormalities. If you’ve had a mammogram before, the radiologist will compare your old mammogram to the new one to look for changes.

What it shows

The procedure produces a black and white image of the breast tissue on a large sheet of film that is interpreted by a radiologist. The doctor reading the films looks for several types of changes: Calcifications are tiny mineral deposits within the breast tissue that appear as small white spots on the films, and are divided into 2 categories:

  • Macrocalcifications – are coarse (larger) calcium deposits that most likely represent degenerative changes in the breasts, such as aging of the breast arteries, old injuries, or inflammations. These deposits are associated with benign (non-cancerous) conditions and do not require a biopsy. Macrocalcifications are found in about half the women over the age of 50, and in about 1 in 10 women younger than 50.
  • Microcalcifications – are tiny specks of calcium in the breast. They may appear alone or in clusters. The shape and layout of microcalcifications help the radiologist judge how likely it is that cancer is present. In most instances, the presence of microcalcifications does not mean a biopsy is needed. Instead, a doctor may advise you to have a follow-up mammogram within 3 to 6 months. In other cases, if the microcalcifications look more suspicious, a biopsy is then needed.

A mass, which may occur with or without calcifications, is another important change seen on mammograms. As with calcifications, a mass can be caused by benign breast conditions or by breast cancer. Masses can be due to many things, including cysts (non-cancerous, fluid-filled sacs) and non-cancerous solid tumors (such as fibroadenomas) but may be cancer and usually should be biopsied if they are not cysts.

A cyst cannot be diagnosed by physical exam nor mammogram alone. To confirm that a mass is really a cyst, either breast ultrasound or removal of fluid with a needle (aspiration) is needed.

If a mass is not a simple cyst (i.e. it is partly solid), then you may have more imaging tests. Some masses can be watched with periodic mammograms, while others may need a biopsy. The size, shape, and margins (edges) of the mass help the radiologist to determine whether cancer may be present.

Your prior mammograms may help show that a mass has not changed for many years, which would mean that the mass is likely a benign condition and help avoid an unnecessary biopsy. Having your prior mammograms available to the radiologist is very important.

A mammogram may show something suspicious, but by itself it cannot prove that an abnormal area is cancer. If a mammogram raises a suspicion of cancer, a small amount of tissue must be removed and examined under a microscope. This procedure is called a biopsy.


What are some tips on having a mammogram?

The following are useful suggestions for making sure that you receive a quality mammogram:

  • Yearly mammograms are recommended starting at age 40 and continuing for as long as a woman is in good health.
  • Use a facility that either specializes in mammography or does many mammograms a day.
  • If you are satisfied that the facility is of high quality, continue to go there on a regular basis so that your mammograms can be compared from year to year.
  • If you are going to a facility for the first time, bring a list of the places, dates of mammograms, biopsies, or other breast treatments you have had before.
  • If you have had mammograms at another facility, you should make every attempt to get those mammograms to bring with you to the new facility so that they can be compared to the new ones.
  • On the day of the exam, don’t wear deodorant; some deodorants contain substances that can interfere with the reading of the mammogram by appearing on the x-ray film as white spots.
  • You may find it more convenient to wear a skirt or pants, so that you’ll only need to remove your blouse for the examination.
  • Schedule your mammogram when your breasts are not tender or swollen to help reduce discomfort and to assure a good picture. Try to avoid the week just before your period.
  • Always describe any breast symptoms or problems that you are having to the technologist who is doing the mammogram. Be prepared to describe any pertinent medical history such as prior surgeries, hormone use, and family or personal history of breast cancer. Also discuss any new findings or problems in your breasts with your doctor or nurse before having a mammogram.
  • If you do not hear from your doctor within 10 days, do not assume that your mammogram was normal. Call your doctor or the facility.

What to expect when getting a mammogram?

  • Most private health plans cover mammogram costs, or a portion of them. Low-cost mammograms are available in most communities. Call the local hospital or the National Cancer Society for information about facilities in your area.
  • Having a mammogram requires that you undress above the waist. A wrap will be provided by the facility for you to wear.
  • A technologist will be present to position your breasts for the mammogram. Most technologists are women. You and the technologist are the only ones present during the mammogram.
  • The whole procedure takes about 20 minutes. The actual breast compression only lasts a few seconds.
  • You may feel some discomfort when your breasts are compressed, and for some women compression can be painful. Try not to schedule a mammogram when your breasts are likely to be tender, as they may be just before or during your period.
  • All mammogram facilities are now required to send your results to you within 30 days. Generally, you will be contacted within 5 working days if there is a problem with the mammogram.
  • Only 1 or 2 mammograms of every 1,000 lead to a diagnosis of cancer. About 10% of women who have a mammogram will require more tests, and the majority only need an additional mammogram. Don’t be alarmed if this happens to you. Only 8% to 10% of those women will need a biopsy, and 80% of those biopsies will not be cancer.
  • Women aged 40 or older should get a mammogram every year. You can schedule the next one while you’re there at the facility and/or request a reminder.

Is mammography really an effective way to detect cancer?
Mammograms aren’t perfect. Normal breast tissue can hide a breast cancer, so that it doesn’t show up on the mammogram. This is called a false negative. And mammography can identify an abnormality that looks like a cancer, but turns out to be normal. This “false alarm” is called a false positive. To make up for these limitations, more than mammography is needed. Women also need to practice breast self-examination (BSE), get regular breast examination by an experienced health care professional (“clinical breast examination”), and, in some cases, also get another form of breast imaging, like ultrasound or MRI scanning.

Is it risky to do a mammogram due to radiation exposure?
The risk of contracting breast cancer by radiation exposure due to mammography is very low. Risk estimates from an annual two view mammography over 10 consecutive years of 100,000 women aged 40 years, result in more than 8 breast cancers during the lifetime of these women. The benefit-to-harm ratio is estimated to be 48.5 lives saved per 1 life lost to radiation exposure. However, the benefits need to be taken into account to balance the discussion of risks. The potential benefits outweigh the risk.

Differences between screening and diagnostic mammograms:

Screening Mammograms

  • Routine
  • Annual or as recommended
  • Asymptomatic (no signs of cancer)
  • Family history of breast cancer
  • Fibrocystic breasts

Diagnostic Mammograms

  • Not routine
  • As needed
  • Symptomatic: breast pain or tenderness; lump or mass; nipple discharge
  • Personal history of breast cancer
  • Previous abnormal mammogram or abnormal physical exam
  • Breast implants
  • Previous breast biopsy or surgery