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benefits and limitations of mammography

No medical test is perfect. All screeningScreening:
The search for diseases such as breast cancer in people without symptoms. Mammography is an important tool for breast cancer screening and earlier detection.
tests, including mammographyMammogram (also called mammography):
a low-dose X-ray of the breast. It is used to take images of the breasts and is an important screening tool for the earlier detection of breast cancer.
, have benefits and limitations. Knowing what they are may help you make an informed decision about what is right for you.


Breast cancer screening aims to reduce mortality ratesMortality (rate):
The number of people that die from a disease in a population over a period of time.
by detecting breast cancer earlier. Breast cancer mortality rates have decreased by 43% since the peak in 1986 as a result of increased access to organized breast cancer screening programs and advancements in screening, diagnosis, treatment.

Mammography is the most commonly used method of breast cancer screening in many places. It has been widely tested and proven to help reduce deaths from breast cancer by 25-35% in women who start screening by mammography from the age of 40. 

Regular screening by mammography offers the following benefits:

The earlier detection of breast cancers

If breast cancers are detected when they are small and have not spread, the likelihood of successful treatment is very high.

Better treatment options 

In most cases, when breast cancer is detected at an early stage there are more treatment options with less invasive treatment (e.g. lumpectomyLumpectomy:
surgery to remove a breast tumor and a small margin of surrounding normal tissue.
rather than mastectomyMastectomy:
surgery to remove all or part of the breast and sometimes other tissue.
), or additional treatments such as chemotherapyChemotherapy:
a treatment method that uses medication to destroy cancer cells.
may not be needed.

Reduced death and disability from breast cancer 

In most cases, the earlier detection and timely treatment of breast cancer reduces the risk of death or long-term disability.

Access to the highest quality screening

When you have a mammogram offered by your provincial or territorial organized breast cancer screening program or at an accredited clinic, you are receiving the highest quality screening. These screening clinics have highly trained staff who specialize in breast cancer detection. They also meet national standards for radiologistRadiologist:
A doctor who specializes in reading tests such as ultrasounds and X-rays. A radiologist may also perform core biopsies and use imaging techniques to guide cancer treatment.
and medical radiation technologist qualifications, equipment, image quality, radiation dose, quality control and quality assurance.

Feeling empowered

By participating in screening you are taking action for your breast health. Screening is an important part of preventive health care and is a concrete action you can take for your breast health. 


Screening aims to reduce mortality rates by finding breast cancer earlier, when there is a better chance of surviving the disease. However, no screening test is 100% perfect. Sometimes a screening test may not be able to show with certainty that there is no cancer, or occasionally may miss breast cancer. While the majority of women who are screened will not have breast cancer, sometimes more information and testing may be necessary to be confident and rule out the disease.

The limitations of breast cancer screening by mammography include:

Need for additional tests

Some test results show something suspicious that is ruled out when further testing is done. About 1 in 10 women may be called back for more testing after their mammogram. These tests may be taken with ultrasoundUltrasound:
an imaging technique that uses sound waves to take a picture of structures in the body, such as the breast.
or MRIMagnetic Resonance Imaging (MRI):
An imaging technique that uses powerful magnetic fields and radio waves to create detailed, 3-dimensional images of the organs and tissues in the body, such as the breast.
. If these test results are also suspicious, a biopsyBiopsy:
a procedure in which tissue samples are removed from the body for examination under a microscope to determine if cancer or other abnormal cells are present.
may be required.  Do not be alarmed if you are called back. Of the 1 in 10 women who require additional testing, approximately 95% will not have breast cancer.

False negatives

Other test results miss breast cancer (this is called a false negativeFalse negative:
some test results miss cancer. This is referred to as a “false negative” result. Regular screening at specific time intervals is the best way to overcome this limitation.
). A false-negative mammogram appears normal even though breast cancer is present. Overall, screening mammograms miss between 1-2 in 10 (or 10-20%) of breast cancers. It can be more difficult to detect breast cancer by mammography alone in women who have dense breasts. This type of screening result may lead to a false sense of security and a delay in diagnosis and treatment.

Regular screening at specific time intervals and at the same location (so the radiologist can compare your results to your previous mammograms) is the best way to overcome this limitation. If you are concerned about a screening result, or if you notice new symptoms or breast changes even if you have recently had a normal screening result, we encourage you to speak to a health care provider.


Some breast cancers that are found by mammography would never become a health problem in the woman’s lifetime (e.g. some cancers grow very slowly). Currently no test exists that can detect which cancers will not threaten the woman’s health from those that will be harmful and must be treated. So, all signs of breast cancer are treated as harmful and therefore some amount of overtreatment occurs. Research is underway to try to determine how to distinguish between the more aggressive and slower growing breast cancers so that each can be treated in the most appropriate way in order to further limit over treatment.

Make an informed decision

To help you make an informed decision about what is right for you, Canadian Breast Cancer Foundation encourages you to learn about your breast health, breast cancer risk, ways to reduce your risk, and the benefits and limitations of breast cancer screening. To inform your decisions, we also encourage you to consider speaking with a health care provider.

Click here for a discussion between leading breast cancer experts on the benefits and limitations of getting a mammogram.


Canadian Breast Cancer Foundation. (2010). Earlier Detection and Diagnosis of Breast Cancer. Recommendations and Scientific Review from It’s About Time! A Consensus Conference. Toronto, ON: Canadian Breast Cancer Foundation.

Health Canada. It’s Your Health: Mammography. Accessed June 23, 2014.

Public Health Agency of Canada. Information on mammography for women aged 40 and older. Accessed June 23, 2014.