Canadian and international guidelines say that most women diagnosed with Stage 1 or Stage 2 breast cancer don't need additional MRIs or CT scans because the risk that their cancer has spread is very low.
And yet a study of all early stage breast cancer diagnoses in Ontario between 2007 and 2012 found that 86 per cent of those women had at least one additional scan after their diagnosis and most had multiple scans.
In fact, the average was nearly four scans per woman. The scans were to see if the cancers had moved into the bones, lungs, abdomen or pelvis.
"I think the bottom line really is that this massive provincial data set tells us that the system has gone astray and now is the time to really help enhance patient care," Dr. Mark Clemons, the paper's senior author, said in an interview.
Clemons is a professor of medicine at the University of Ottawa and a clinician at the Ottawa Hospital. The study is published in this week's Canadian Medical Association Journal.
Multiple evidence-based guidelines that are issued to help doctors make decisions about the appropriate way to practise advise against doing additional tests on women with Stage 1 or 2 breast cancer to see if their cancers have spread.
Those guidelines don't apply if the women have symptoms that would suggest their cancers have progressed — things like back ache or shortness of breath. But metastasis — spread — is rare when breast cancer is detected in the early stages, Clemons said.
In fact, the chances that a Stage 1 patient will have metastases that can be picked up on a scan are remote — 0.2 per cent, the study says. For Stage 2 breast cancer, the rate is just 1.2 per cent.
Given how unlikely it is that the cancer will have spread, expert groups have concluded the risks associated with additional imaging tests outweigh the benefits women might get from them.
For the individual women, those risks include unnecessary exposure to radiation — which is itself a cancer risk — as well as the fact that their treatment might be delayed as their doctors wait for the results of the additional tests.
The unneeded tests also create problems for the health-care system and for patients with other diseases who need MRIs and CT scans.
"It actually shows that doing more is certainly not better," Clemons said of the study.
"We've actually shown harms are being done to these patients, harms such as delaying starting treatment. It means more radiation exposure, more anxiety for patients. The costs are millions of dollars a year.
"And also another interesting harm is the fact that by patients having scans that they don't need, we're actually delaying other patients with other diseases from getting investigation they require."
Clemons said the researchers cannot tell from the data why women are getting so many tests against the advice of the practice guidelines. The group is conducting a study in which they are talking to women and doctors to uncover what is behind the decisions to order the extra testing.
"If we can find out why ... we can then implement strategies, which are evidence-based strategies, to change this pattern," he said.
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