Recently, Canadian Medical Association Journal (CMAJ December 10, 2018) published new recommendations on screening for breast cancer in women aged 40-74 years who are not at increased risk for breast cancer.
These guidelines apply to women with no previous history of breast cancer, no history of the disease in a first-degree relative like a mother or sister, no known BRCA genetic mutation and no previous exposure to therapeutic radiation of the chest wall.
The recommendations come from the Canadian Task Force on Preventive Health Care. The new recommendations update guidelines first published in 2011. The guidelines are summarized below:
1. There should be no routine mammography for most women aged 40 to 49 because the risk of cancer is low in this group while the risk of false-positive results and overdiagnosis and overtreatment is higher.
2. Routine screening mammography should be done every two to three years for women aged 50 to 69.
3. For women aged 70 to 74, routine screening mammography should be done every two to three years.
4. MRI and ultrasound should not be used for screening purposes.
5. Routine clinical breast examinations or breast self-examinations to screen for breast cancer is discouraged.
Although we rely on mammography for screening the fact remains it is not a perfect screening tool. Screening may lead to overdiagnosis, resulting in unnecessary treatment of cancer that would not have caused harm in a woman’s lifetime and false-positive results that can lead to both physical and psychological consequences. Overdiagnosis and false-positives with subsequent biopsies are more common in younger women.
Other risks and limitations of mammograms include: exposure to low-dose radiation, having a mammogram may lead to additional testing in about 10 per cent of cases. Mammograms can miss one in five cancers in women.
On the other hand, mammography is the only technique proven to be safe and effective in screening for breast cancer, and mammography equipment is the only imaging technique licensed by Health Canada for breast cancer screening. It is good at finding breast cancer, especially in women ages 50 and older. Overall, the sensitivity of mammography is about 87 per cent. Screening may identify breast cancer earlier and lead to more effective and less invasive treatment.
What about women aged 40 to 49 years? Research shows balance of benefits and harms from screening is less favourable for women in this age group than for older women. If a woman in this category requests a mammogram then the guidelines suggest she should not be denied.
Death rates from female breast cancer dropped 40 per cent from 1989 to 2016. Since 2007, breast cancer death rates have been steady in women younger than 50, but have continued to decrease in older women (www.cancer.org).
You may ask, if none of the screening tests are perfect then why is there a decline in the death rate from breast cancer?
A review article in the Lancet Oncology (Why is breast-cancer mortality declining? April 2003), the authors argue that although some of the decline in breast-cancer mortality is due to a reduction in breast-cancer risk, most of it can probably be attributed to adjuvant systemic therapy and the earlier detection of palpable tumours. The authors also explain in the article why advances in the treatment of breast cancer might be outpacing the value of mammography screening.
Important thing to remember is new guidelines empower women to be in charge of their own screening protocol. The final decision on whether to be screened should fall to the patient as long as that patient understands the risks. Patients should be left ultimately to decide what is best for them.
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