Women don’t need to follow a rigid schedule for breast cancer screening and doctors should inform patients of the potential risks mammograms pose, according to new national screening guidelines released Monday.
The new guidelines recommend women aged 50 to 74 who don’t have a family history or other factors that put them at increased risk of breast cancer get mammograms every two to three years, but with a caveat: The decision to have a mammogram should be based on “the relative value that a woman places on possible benefits and harms from screening.”
In other words, women should decide for themselves, with guidance from their health-care provider, whether to get screened. Similar to earlier guidelines published in 2011, the new ones do not recommend breast screening for women under age 50 who are not at an increased risk of breast cancer because the evidence shows the potential risks outweigh the benefits.
“In the past, it has been more of a tick box, an automatic, you’re this age and you head for a mammogram,” said Donna Reynolds, a family physician who is a member of the Canadian Task Force on Preventive Health Care that wrote the guidelines. “We need to do a better job of informing women about the risks and the benefits of having [screening mammograms]."
The guidelines, published Monday in the Canadian Medical Association Journal, reflect a growing trend in health care to reduce unnecessary screening, tests or procedures that may have limited benefit. In the case of breast cancer, screening mammograms can help detect the disease in some women, but others may experience false positives and unnecessary follow-up tests and treatments as a result. Mammograms also come with the risk of overdiagnosis – they may detect some forms of cancer that would never have developed into a significant health risk.
According to evidence cited in the new guidelines, mammograms will result in 0.75 fewer deaths per 1,000 women over a seven-year period. Research indicates that 25 per cent of invasive and non-invasive cancers detected by screening mammograms over five years are overdiagnosed.
Lisa Del Giudice, Cancer Care Ontario’s regional primary cancer lead, said the new recommendations are an important signal to women that they are ultimately responsible for deciding whether to get screened.
“It leaves it open to allow women to have that autonomy to decide if this is the right test,” said Dr. Del Giudice, who also works as a family physician based at Toronto’s Sunnybrook Health Sciences Centre.
She highlighted the fact that the death rate from breast cancer has steadily fallen in recent decades as a result of better screening, but also due to advancements in cancer care and greater awareness among women to report breast changes to their doctors. While mammography is a useful screening tool, Dr. Del Giudice said it plays a limited role.
“I think women have overestimated just how much that benefit [of screening mammography] is,” she said.
The task force reviewed studies of how women perceive the risks and benefits of breast cancer screening before writing the guidelines. What they found is that among women 40 to 49, many decided to forgo screening once they learned of the relatively high risk of false positives, unnecessary follow-up and overdiagnosis. For women 50 and older, many decided to undergo screening after learning that mammograms could pose risks, but also may reduce their overall mortality rate from breast cancer.
The guidelines also note that while breast density may be a risk factor for cancer, it’s difficult to identify and gauge the density of breast tissue. Using unreliable methods to study breast density could expose women to unnecessary false positives and follow-ups, according to the recommendations.
Women should not undergo magnetic resonance imaging (MRI) scans, tomosynthesis, a type of three-dimensional mammogram, or ultrasound to screen for breast cancer, the guidelines state. There is no evidence to back up use of these screening methods and they “would require the use of substantial and scarce health care resources."