Too many people with late-stage cancer are being unnecessarily screened for new forms of the disease, exposing them to side effects and stress, as well as adding strain on the health-care system, concludes a new study.

Additional screening also eats up time that individuals could be using to spend time with family or focus on treatment for their disease, according to the authors of the study published Monday in the journal CMAJ Open.

“These are patients who are already quite ill who should be focused on their own quality of life and fighting their cancer, but instead they’re going through tests that potentially have side effects associated with them … but certainly also likely not to offer them any benefit,” said study co-author Matthew Cheung, hematologist at the Odette Cancer Centre at Sunnybrook Health Sciences Centre in Toronto.

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The researchers looked at nearly 21,000 patients with stage IV metastatic lung, breast and prostate cancer. Stage IV cancer is often referred to as advanced cancer and while it typically can’t be cured, treatments can help manage symptoms and delay progression.

Within one year of diagnosis, a significant number of those patients were screened for colorectal cancer: about 3 per cent of lung cancer patients, more than 6 per cent of breast cancer patients and 13 per cent of prostate cancer patients. After three years, those numbers jumped even higher: more than 4 per cent of lung cancer patients, 12 per cent of breast cancer patients and 27.5 per cent of prostate cancer patients had undergone colorectal cancer screening.

Choosing Wisely Canada, a campaign to reduce unnecessary tests and treatment, advises against cancer screening in patients who have already been diagnosed with late-stage metastatic cancer. The campaign was not officially involved in this study, but the researchers wanted to see whether the recommendation was being followed in Canada. The fact that such a substantial number of those patients are being screened, however, suggests there’s a lot of room for improvement, according to Dr. Cheung, who is also an adjunct scientist at the Institute for Clinical Evaluative Sciences in Toronto.

The risk of death from late-stage metastatic cancer tends to be high, so screening patients for new forms of cancer is "an inappropriate use of scarce health-care resources,” the researchers wrote.

“Not only does that involve a system cost, but it involves a cost to the patient,” said Simron Singh, study co-author and medical oncologist at Sunnybrook’s Odette Cancer Centre.

He said unnecessary screening of cancer patients “is not the sort of care we want to provide” and that it’s up to patients and care providers to have these conversations. It’s unclear how many medical professionals are following the Choosing Wisely recommendations, but he said the campaign is being discussed more frequently.

“I certainly think it’s part of the conversation,” Dr. Singh said.