Breast cancer screening

Studies by the Ministère de la Santé et des Services sociaux and the Institut national de santé publique du Québec show the advantages, disadvantages and limitations of mammography.

The Québec Breast Cancer Screening Program (PQDCS) is for women aged 50 to 69. All women eligible for this program should learn about the advantages, disadvantages and limitations of mammography. Each can then make an informed decision about whether to participate in the PQDCS or not.

Women who participate in the Program when they turn 50 will be invited to have a mammogram every 2 years for a period of 20 years, when they reach 69.

Advantages

Breast cancer screening every 2 years over a 20-year period:

• Reduces the risk of dying from breast cancer
  Of 1,000 women who have a mammogram every 2 years for 20 years, 7 deaths are prevented
• Reduces the risk of having to undergo chemotherapy
  Screening often allows for the detection of cancers at an early stage of development. Treatment is then possible without chemotherapy.
• Allows women to know the health of their breasts
  The vast majority of women (nearly 98 %) will not have breast cancer if their mammograms and additional examinations do not reveal cancers.

Disadvantages

Breast cancer screening every 2 years for 20 years can lead to:

• Periods of waiting and anxiety when additional examinations are required
  Almost half the women who participate in the screening for 20 years (453 in 1,000) have at least one additional examination. This represents 156 more women than in the 1,000 who do not participate in the screening.
• Possible overdiagnosis
  Of 77 breast cancer diagnoses, 10 would be cases of overdiagnosis.

Overdiagnosis is the discovery of a cancer that would never have been detected without screening. It can happen that a woman receives a diagnosis for cancer that would never have had an effect on her health or consequences on her life – like a cancer that develops very slowly or a benign cancer. This could happen to participants in the screening program because a mammogram detects breast cancer in the early stages of development.

However, given that it is still impossible to differentiate between harmless cancers and deadly ones, all cancers are treated. As such, women in the screening program could:

• Receive treatment that would not be necessary
• Suffer the side effects of these treatments
• Have to live with the experience of having been diagnosed with cancer
• Have frequent medical appointments to ensure that the cancer does not return

Limitations

Breast cancer screening every 2 years for 20 years does not guarantee:

• That all breast cancers will be detected
  Of 1,000 women who have a mammogram every 2 years for 20 years, 77 will be diagnosed with breast cancer. Of these, 21 will be diagnosed with cancer even though their mammography results were normal. Such a situation can occur if:
  • The cancer was not visible on the mammogram
  • The cancer was not yet developed at the time of the mammography
• That all participants with breast cancer will survive
  Of 1,000 women who have a mammogram every 2 years for 20 years, it is estimated that 13 will die of breast cancer.

Also, a mammogram is an X-ray. Like all X-ray examinations, radiations are emitted. According to several studies, the risk of breast cancer due to radiation emitted during a mammogram is very low in women aged 50 to 69 who participate in screening.

A few statistics

In comparing 1,000 women aged 50 to 69 who participate in the screening program every 2 years for 20 years to 1,000 who do not participate, several differences are apparent.

Of 1,000 participants:

• 453 women must have additional examinations
• 77 women are diagnosed with cancer
• 10 of those diagnosed with cancer would be cases of overdiagnosis
• 13 women die from breast cancer

Of 1,000 non-participants:

• 297 are prescribed breast exams by their doctor due to signs and symptoms
• 54 women are diagnosed with cancer
• No cancer is a case of over-diagnosis
• 20 women die from breast cancer

In other words, of 1,000 women aged 50 to 69 screened every 2 years for 20 years:

• More women have additional examinations (156 more)
• More cancers are discovered (23 more)
• Cancers found would be cases of overdiagnosis (10 more)
• There are less breast cancer deaths (7 less)