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Benefits and Potential Harms

For women of average risk research shows that the benefits of breast cancer screening with mammography outweigh the potential harms. BreastCheck recommends that most women age 50 – 74 have a screening mammogram every 2 years.


Mammography screenResearch shows that regular screening mammograms reduce deaths from breast cancer in women 50 to 74 years of age by 20-30%.

This is due to early detection. Most breast cancers discovered through regular screening are found at an earlier stage when there may be more treatment options as well as more positive outcomes.

Potential Harms

Breast screening does not prevent breast cancer. A mammogram can only find breast cancer if it is already there. Some women may develop breast cancer before their first mammogram or between mammograms.

Mammograms do not find all breast cancers. 20 out of every 100 breast cancers cannot be seen on a mammogram, some cancers are very difficult to see on a mammogram, and/or the radiologist reading the mammogram may miss a cancer (this happens occasionally no matter how experienced the doctor is). It is important to know how your breasts normally look and feel. Contact your health care provider if you notice any changes in your breasts between screening appointments, even if you had a normal mammogram.

About 5 out of every 100 women screened at BreastCheck will be sent for further tests. Only 1 of these 5 women will be diagnosed with breast cancer. Although this is a normal part of the screening process, going for further tests may cause anxiety and worry.

Mammograms are not guaranteed to save your life. Not all breast cancers found at screening can be cured. Some women will die of breast cancer even though it was found by a screening mammogram; some will die of something else before they would die of breast cancer. For these women, their quality and length of life may not be increased by finding the breast cancer. There is no way to know which women will fall into these groups and which women will be truly helped by screening.

The Public Health Agency of Canada has a Decision Aid (pdf) for women ages 40 and older that further explains the benefits and possible harms of breast cancer screening.


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