The Canadian Task Force on Preventive Health Care recommends that women aged 50–74 schedule a mammogram every 2–3 years.i
High risk refers to women who have a personal or family history of breast cancer, and/or a gene mutation known as BRCA1 or BRCA2, and/or prior chest wall radiation. The BRCA1 and BRCA2 gene mutation greatly increases a person’s risk of breast cancer. This guideline does not apply to women with a high risk of breast cancer. If you are high risk, consult a physician about the best screening options for you.
Breast cancer is the second most common cause of cancer deaths among women aged 40–79. In 2010, approximately 80% of new breast cancer cases diagnosed in Canada were in women older than 50, and of those, approximately 28% were in women 70 or older.
Breast cancer screening is trying to detect cancer when symptoms are not present.
The most common method of breast cancer screening is with a special x-ray called mammography. A mammogram takes x-ray images (film or digital) of the soft tissue of the breast to look for signs that breast cancer may be developing, even if there are no previous symptoms. Other methods such as ultrasounds are also used under certain circumstances, but mammography has been shown to be the most effective method of screening for breast cancer in its early stages.
Detecting cancer requires tests such as mammography (x-rays) and biopsies (taking a sample of the breast tissue to look for signs of cancer under a microscope). Because these tests are not always accurate, screening can lead to unnecessary testing or breast surgery in women without cancer. However, it can also prevent unnecessary deaths in women who have breast cancer that has not yet been detected. Some of the harms that can be associated with mammography are false positives, where a screening test indicates that you might have cancer when in fact you do not. False positive results may lead to anxiety, unnecessary biopsies, lumpectomy (removing a lump in the breast, whether cancerous or not) and/or mastectomy (removal of a breast).
Screening with mammography modestly reduces the number of deaths from breast cancer, with the greatest impact being in women 50–74 years.
The Task Force looked at the best evidence from around the world and found that there was a modest reduction in deaths due to the detection of breast cancer by mammography for women 50–74, as well as a lower risk of false positives when compared with women 40–49 years.
The recommendation to screen every 2–3 years is based on evidence that takes into account the associated harms of screening and found no difference in benefit (ie: reducing the number of deaths) between screening every 2–3 years and screening annually. This recommendation is similar to guidelines from the United Kingdom (every 3 years) and the United States (every 2 years).
The chance of getting breast cancer is lower and the chance of having a false positive mammogram is higher in the 40–49 age group, which can lead to further investigation, including other unnecessary procedures such as breast removal. We recommend not screening in women aged 40–49, however women in this age group who are interested in screening and less concerned about its undesirable consequences should discuss their options with a physician.
For women aged 75 and older it is possible that routine screening with mammography may, over time, reduce the number of deaths from breast cancer, however not enough data was available to make a clear recommendation. We suggest discussing the benefits and harms of mammography with a physician, who will consider the individual patient’s overall health.
The Task Force recommends against routine BSE (self-examination of the breast) and CBE (examination performed by a health professional), after their review found that neither reduced breast cancer or related deaths in women aged 40–74. Furthermore, two large studies identified no reduction in deaths from breast cancer associated with teaching BSE to women aged 31 to 64, but found evidence of increased harm.