what you need to know about the controversy over breast-cancer screening
5 minute read
in 2020, an estimated 27,400 women in canada were diagnosed with breast cancer; 5,100 died from the disease
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plastic surgeon dr. toni zhong, the inaugural belinda stronach chair in breast cancer reconstructive surgery at toronto’s university health network, is seeing younger and younger women in her practice, women with tumours or masses that are quite large, and that have sometimes already spread into the lymph nodes.
they’re women who, because they’re younger than 50, were not getting regular mammograms, “and, when you’re not screened, you’re not detecting breast cancer early,” zhong said.
an american health panel’s draft recommendation that women should start getting mammograms at age 40, rather than 50, has stirred up a hornet’s nest in canada, sparking fresh debate over the optimal starting age for screening mammograms.
“on the surface, more cancer screening should be better,” dr. christopher labos, a montreal physician and co-host of the body of evidence podcast, wrote in the montreal gazette. but more isn’t always better, labos said.
the task force behind canada’s current screening guideline, which endorses regular screening of women 50 and older only, was given $500,000 in extra funding by ottawa this week to fast-track its update of their 2018 guideline. a new draft guideline is due to be released in late fall.
“with 12 per cent of women in canada expected to be diagnosed with breast cancer in their lifetime, having breast cancer screening guidelines that are based on the latest science is essential,” federal health minister jean-yves duclos said in a statement.
in 2020, an estimated 27,400 women in canada were diagnosed with breast cancer; 5,100 died from the disease.
here’s a look at what to know about the controversy over breast-cancer screening.
what’s a mammogram and why is it done?
it’s an x-ray of the breast that looks for early signs of breast cancer before they can be felt. it’s also used to detect and diagnose breast cancer in women with symptoms, like a lump or pain.
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“the language needs to be very clear,” zhong said. “when we talk about screening mammography, we’re talking about asymptomatic patients versus someone who presents to their family doctor with a lump or something that would suggest breast cancer. that’s no longer screening, that’s diagnostic mammography.”
every woman is different.
“but, generally speaking, a tumor is about two centimetres before one can palpate or detect it with one’s own fingers,” zhong said. “a mammogram can see things that are just millimetres — very, very early changes.”
if an abnormality is spotted, and there’s a high suspicion of cancer, tissue will be removed for biopsy.
why are mammograms in the news?
last month, the u.s. preventive services task force posted draft recommendations advising mammograms every two years for all women, starting at age 40. the influential panel previously recommended screening every other year by age 50, though it said women in their 40s could make an individual decision about when to start screening.
lowering the starting age could result in 19 per cent more lives saved, according to the panel, which also noted that black women are 40 per cent more likely to die of breast cancer than white women “and too often get deadly cancers at younger ages.”
are other women getting cancer at younger ages?
the number of newly diagnosed breast cancers in american women in their 40s has been increasing about two per cent each year, john wong, a professor of medicine at tufts university school of medicine told the washington post.
in canada, breast cancer diagnoses among women in their 40s have grown by 1.6 per cent per year since 2015, according to statistics canada.
what do the canadian guidelines recommend?
the guidelines for average-risk women who don’t have a history of the disease, a genetic predisposition or other risk factors recommend no routine screening for women aged 40 to 49.
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funded by the public health agency of canada, the canadian task force on preventive health care, an arm’s-length body, said that overdiagnosis and false positives are more common in younger women, exposing them to unnecessary and potentially harmful interventions.
among 1,000 women aged 40 to 49 screened over seven years, 294 will receive a false-positive result; 43 will undergo a biopsy.
overdiagnosis means detecting slow-growing cancers that would never have caused a problem in a woman’s lifetime.
the panel estimated that the absolute benefit of screening women under 50 would mean 0.58 fewer deaths per 1,000 women screened over an average of seven years and that 1,724 women would have to be screened to save one life.
“the balance of benefits and harms from screening is less favourable for women aged 40 to 49 than for older women,” the panel concluded.
however, the recommendation was based on “low-certainty evidence” from trials in sweden, canada, the u.s. and the united kingdom dating back from 1963 to 1991.
“we can’t apply scientific evidence from 30 years ago to women today,” zhong said.
concerns have also been raised about the risk of bias, and the way some women were randomized to different groups.
how has the panel responded to the new u.s. draft recommendations?
“the primary goal of the (canadian) guideline update is to ensure that canadian recommendations reflect the latest knowledge and best practices,” the panel said in a statement. “it’s important to note that recommendations from other countries should undergo proper review and scrutiny before being adopted in canada.”
not screening younger women is costing lives, zhong and other doctors argue.
“every month that we delay a decision to expand screening to women aged 40-49 in ontario, we lose another 13 young women in the prime of their lives,” dr. david jacobs, a radiologist at humber river hospital in toronto and president of the ontario association of radiologists, wrote in a commentary published by the national post.
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a university of ottawa-led study last year found that women who aren’t screened in their 40s are presenting with later stage breast cancer in their 50s, meaning more intensive treatment, and a worse prognosis.
the five-year survival rate for early breast cancer, where the cancer is small, it’s localized, it hasn’t travelled beyond the borders of the breast is over 90 per cent, zhong said. “once it gets into the lymph nodes, (five-year) survival becomes much less — 70 per cent or lower.”
a biopsy to confirm, or rule out, cancer, is minor surgery. it’s uncomfortable. sometimes it causes a hematoma, or bruising, or pain for several weeks afterwards. it’s not without some level of physical trauma, zhong said.
“but if it’s found to be breast cancer, and it’s early, it can save you from chemotherapy; it can save you from radiation. it can perhaps even save your life.”
editor’s note: this story was corrected from its original version to clarify that breast cancer diagnoses among canadian women in their 40s has increased 1.6 per cent a year since 2015.
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