Breast Cancer

Breast cancer is the most common cancer in Canadian women, with one in nine women expected to be diagnosed with it in their lifetime. In 2014, it is estimated that about 9,800 Ontario women will be diagnosed with breast cancer and that 1,900 will die from this disease.

Who is eligible for screening?

Screening is available for two groups of women

  1. Women aged 50 to 74 who are at average risk for breast cancer with mammography every two years
  2. Women aged 30 to 69 years who are identified as being at high risk for breast cancer with annual mammography and breast magnetic resonance imaging (MRI) screening

Breast cancer occurs primarily in women 50 to 74 years of age (57% of cases). Most women diagnosed with breast cancer have no family history of the disease.

Who is considered high risk?

Less than 1% of women in the general population are estimated to be at high risk for breast cancer. Women are considered to be at high risk for breast cancer and eligible for screening if they have no acute breast symptoms, are 30 to 69 years of age and meet one of the following risk criteria:

  • Are known to be carriers of a deleterious gene mutation (e.g., BRCA1, BRCA2)
  • Are the first degree relative of a mutation carrier (e.g., BRCA1, BRCA2) and have declined genetic testing
  • Are determined to be at ≥ 25% lifetime risk of breast cancer -- must have been assessed using either the IBIS or BOADICEA risk assessment tools, at a genetics clinic
  • Have received chest radiation treatment (not chest x-ray) before age 30 and at least 8 years previously.

Women at high risk have a greater estimated lifetime risk of developing breast cancer (up to 85%) than the general population (10-12%).

Women at high risk develop breast cancer at an earlier age and their breast cancers tend to be more aggressive than breast cancers diagnosed in women at average risk.


  1. "OBSP Screening for Women at High Risk", Cancer Care Ontario, accessed April 20, 2017 from
  2. "About the Ontario Breast Screening Program", Cancer Care Ontario, accessed April 20, 2017 from

How is screening performed?

Breast cancer screening is the regular examination of a woman's breasts to find breast cancer early. The best screening test for most women is the mammogram. A mammogram takes an X-ray picture of the breast and can find changes in the breast even when they are too small to feel or see. For most women, the mammogram results will be normal.

For women at high risk, screening with breast magnetic resonance imaging (MRI) will be used in addition to mammography (MM)

What happens during the mammogram?

  1. A registered medical radiation technologist specializing in mammography places the patient's breast on a special X-ray machine.
  2. A plastic plate is pressed down slowly to flatten their breast and hold it in place for a few seconds.
  3. Four pictures are taken, two of each breast.
  4. The technologist will check the pictures to make sure they are good enough quality for the radiologist to read. If needed the technologist will take additional pictures.
More information about mammograms

Where do people go for screening?

Women aged 50 to 74 years can call the nearest OBSP screening location to make an appointment (a doctor’s referral is not needed).

View map of screening locations


  1. "Mammograms," Cancer Care Ontario, accessed April 20, 2017 from
  2. "OBSP Screening for Women at High Risk", Cancer Care Ontario, accessed April 20, 2017 from

How is screening encouraged?

Letters about breast cancer screening are mailed to eligible women ages 50 to 74.

These letters invite eligible women to get screened for breast cancer, remind them when it’s time to get screened again and inform them of their screening test results. The letters encourage women to speak to their healthcare provider about their screening options and to follow-up on their screening test results, if necessary.

Learn more about breast cancer screening letters

How many people get screened?

The visualizations on this page begin by looking at screening rates throughout Ontario. This serves to give an idea of the absolute and relative numbers of people who are overdue for screening, and where they are concentrated.

The later visualizations add context to this data by displaying the incidence and mortality rates of breast cancer, as well as risk factors divided by regions of Ontario.

Breast Cancer Screening Rates

This visualization shows screening rates divided by region of Ontario. The hexbinplot displays regions of Ontario as equally-sized hexagons, where darker colours indicate higher number of people overdue for screening. The stacked bar chart shows the same data, where the grey values are people who have been screened, coloured bars are overdue for screening, and the total length of the bar shows the number of people eligible for screening. Hover over the bars to display more information.

Incidence and Mortality Rates for Breast Cancer

These graphs display incidence and mortality rates. The hexbinplots show rates from 2010-12 combined, divided by region and age groups. The line graphs indicate changes in rate over a three-year period, divided by age groups.

Demographic information

These graphs show socio-demographic variables and chronic disease risk factors for regions in Ontario. The hexbinplots show the percentage of the population in each region with each risk factor. The heatmaps show the same data as a table, including multiple years when available. To sort the heatmap, click on the rows and columns.


  • Region refers to either Ontario or one of the Local Health Integration Networks (LHINs) in Ontario. The Ontario statistics excluded cancer cases of unknown residence. Therefore, provincial statistics may not match the true counts and rates published elsewhere.
  • Age refers to the age at diagnosis for the cancer.
  • Year refers to the calendar year in which a cancer was diagnosed.