Santé Montréal

Breast Cancer Screening

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A few words about breast cancer

Breast cancer is the most common cancer among women. In 2013, there were an estimated 6000 new cases of breast cancer in Québec. This cancer, which results from the multiplication of abnormal cells in the breast, is the second leading cause of cancer death in women. Men can develop breast cancer but it is rare (1%).

The breast cancer death rate has dropped over the past 10 years. New treatments and regular screening are the main reasons why the rate is going down. 

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When to Consult

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Protection and prevention

Screening mammograms

A mammogram is an x-ray of the breast. Two images of each breast are taken (horizontal and side views).  Mammograms are done by a radiology technician while the woman stands (or sits, if the woman is disabled). The breast is compressed between two plates for a few seconds. The mammogram produces an image of the interior of the breast. A radiologist then reads the films. 

Difference between screening mammograms and diagnostic mammograms

A screening mammogram is used to screen women who don't have any apparent signs or symptoms of breast cancer. This examination can detect breast cancer at an early stage. A diagnostic mammogram is done when a woman has signs or symptoms of breast cancer (e.g. lump, discharge, redness).  

Benefits of mammograms

  • Reduce breast cancer mortality 

The main goal of screening and of mammograms is to reduce breast cancer deaths in women. We have seen a decline in mortality among women aged 50 and over who get screened regularly (every 2 years).

  • Increase chances of being cured

Mammograms are known to be effective to detect breast cancer at an early stage. They can detect smaller cancers, which are easier to treat (see the Canadian Cancer Society's Thingamabob site for more details).

  • Reduce the need for heavy treatment

Mammograms reduce the probability of needing heavy treatment (chemotherapy) or mutilation (removal of the entire breast).

  • Keep track of your health

Regular screening mammograms help keep track of the health of your breasts. 

Inconveniences and limitations of mammograms

Like any medical exam, the mammogram is not perfect.

Risk of overdiagnosis

  • Additional examinations (false positive): When a mammogram result indicates a problem, a woman must then have additional tests. In 90% to 95% of cases, these examinations confirm that there is no cancer. They can, however, cause women to worry and even deter them from getting their next mammogram. Yet, additional tests are essential to make sure there is no cancer in the breast.
  • Overdiagnosis: Some cancers detected with mammograms will never cause death: this is called a diagnosis. Breast cancer is a complex illness and there is no way to know how it will change over time. Some tumours grow very slowly and don't endanger a woman's life; others evolve very quickly. Therefore, it is preferable to treat the cancer. It is estimated that 10 in 1000 women receive unnecessary treatments for breast cancer. 

Risk of underdiagnosis

  • Breast cancer invisible on mammograms (false negative): In some cases, a cancer might not show up on a mammogram even though it is there.
  • Interval cancer: It is possible for breast cancer to develop between two mammograms. This is called "interval cancer". It is quite rare, and women might have a false sense of security during the interval period. Regular, adapted screening is the best way to deal with these inconveniences.


Mammogram machines emit low doses of radiation. The risk of developing breast cancer due to exposure when having a mammogram every 2 years is very low. Research shows that the benefits of screening outweigh the risks of being exposed to low doses of radiation.


For some women, having a mammogram can be uncomfortable, even painful. It is important to know that the breast is compressed only for a few seconds and discomfort disappears right away once the breast is released.Here are a few tips to help prepare for a mammogram and limit discomfort:

  • Make an appointment to have a mammogram 10 days after your period starts.
  • Avoid coffee, tea, chocolate and colas for 2 weeks before your mammogram.



The decision to have a mammogram is yours, and yours alone.
If you are unsure, talk it over with your doctor or another health professional. 

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Risk factors

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Help and Resources

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People at Risk

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Dernière mise à jour le : 2019.03.18