Two new Canadian studies are raising doubts about the benefits of some expensive imaging tests, finding they may not only fail to detect life-threatening disease in certain patients, they can also add to their stress.
One study found the vast majority of women with early-stage breast cancer undergo imaging tests to look for metastasis, or cancer spread, even though international guidelines recommend against such testing. That's because the risk that early-stage breast cancer has spread is low.
The study looked at data on more than 26,000 Ontario women with early breast cancer and found that most had undergone three or more extra imaging tests, such as CT scans (computerized axial tomography) and MRIs (magnetic resonance imaging).
Studies, though, have shown that the chance of Stage 1 breast cancer spreading is only about 0.2 per cent, and 1.2 per cent for Stage 2.
The authors say the problem with these extra tests is they carry a high chance of resulting a false-positive – that is, finding something that turns out not to be cancer. What's more, the extra tests unnecessarily expose women to radiation, and can delay the start of their treatment. As well, the tests may delay other patients who need access to CT scans and MRIs.
Surgeons and oncologists often order extra tests in order to reassure newly diagnosed cancer patients that they are not at risk of dying, which is laudable, write two doctors from Queen Elizabeth II Health Sciences Centre and Dalhousie University in a related commentary. But they say the tests usually mean long wait times for results and more anxiety for patients and their families.
"For most patients with newly diagnosed Stage I and II breast cancer, reflexively ordering staging investigations does not help relieve stress, nor does it detect disease," the commentary authors write in the Canadian Medical Association Journal.
Tests not helpful for blood clots
Another Canadian study found that offering people with unexplained blood clots a CT scan to look for signs of cancer does not actually improve cancer detection.
Thousands of Canadians are diagnosed with a blood clot, or venous thromboembolism, in the lungs and legs each year. Often, the clots are caused by trauma, prolonged periods of not moving, or surgery, but in approximately half of cases, the cause of the blood clot is unknown.
Because studies have suggested that up to 10 per cent of patients with unexplained clots will be diagnosed with cancer within the year, some guidelines recommend a CT scan of the abdomen and pelvis to look for tumours. That’s on top of regular cancer screening protocols that include blood tests and a chest X-ray.
This study looked at more than 850 patients with blood clots; half had regular cancer screening and half also had a CT scan. There was no difference in the number of new cancers detected in the two groups; approximately four per cent of patients from each group were diagnosed with cancer within the next year. There was also no difference in the number of cancer-associated deaths.
The full results appear in the New England Journal of Medicine.
"Although it is tempting to believe that more cancer screening is always better, our study shows that this is not necessarily the case, the study's lead author Dr. Marc Carrier, a hematologist and researcher at The Ottawa Hospital, said in a statement.
"And in fact, unnecessary CT scanning has real risks. It can cause stress and anxiety in patients, as well as radiation exposure, and it can lead to over-investigation of false-positive findings."
The authors speculate that that the reason that cancer was found in only four per cent of patients instead of the 10 per cent noted in previous studies may be because there have been improvements in other kinds of cancer screening.
