invasive weed
Cancer, like an invasive weed, can grow quickly and can spread unless it is controlled. Delays in treatment make it harder to treat by providing more time for it to progress. (Photo: iStock)

Cancer can start from a single defective cell, growing and spreading until it is eventually found through routine screening or once it begins to cause symptoms.

Medical imaging technologies can then be used to find the tumour, and help create a treatment plan.

But the cancer does not stop growing just because a doctor found it and scanned it – the cancerous cells will continue to grow and spread between the time it was imaged and when treatment begins.

Dr. Jean-Pierre Bissonnette, affiliate scientist at UHN's Techna Institute for the Advancement of Technology in Health, led a team to evaluate the spread of non-small-cell lung cancer in 181 patients in a multi-centre international study.

All patients had a positron emission tomography/computed tomography (PET/CT) scan at the time of their diagnosis. PET/CT is a very sensitive imaging method that is able to find and localize even small clusters of cancerous cells. However, due to its cost, patients are rarely scanned again before their treatment begins despite the fact that several weeks can pass between diagnosis and treatment.

For all participants in the study, the research team repeated the PET/CT scans immediately prior to therapy. They then calculated the odds that a patient's cancer had grown enough to move up to the next "stage" – a four-point scale to that reflects how aggressive and widespread a patient's cancer is – in the time between diagnosis and treatment.

After 22 days, there was a greater than five per cent chance that the cancer had moved to a more severe stage; after 42 days there was a 15 per cent chance.

Jean-Pierre Bissonnette
The lead author of the study, Dr. Jean-Pierre Bissonnette, is an affiliate scientist at the Techna Institute for the Advancement of Technology for Health (Techna).

These results raise serious concerns for those on the waiting list for cancer treatment.

For 10 per cent of all patients participating in the study, their cancer had spread so much in the time between diagnosis and treatment that they required changes to their treatment plan. That suggests that many patients who do not receive a second PET/CT scan may be receiving suboptimal treatment for their lung cancer.

"Our data suggests that treatment should commence within three weeks of diagnostic imaging," Dr. Bissonnette says. “Patients with adenocarcinoma or who started at stage IIIB/IIIC are particularly at risk of progressing as they wait for treatment, and it may make sense to prioritize those patients.

"This information is particularly relevant now, as the COVID-19 pandemic has resulted in significant delays in access to diagnosis and therapy for cancer patients."

This work was supported, in part, by The Princess Margaret Cancer Foundation.

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