Research that helps real people, every day

Dr. Marc Carrier, Hematologist and Senior Scientist at The Ottawa Hospital.
Dr. Marc Carrier, Hematologist and Senior Scientist at The Ottawa Hospital. (photo credit: Mark Holleron)

Imagine that you are one of the thousands of people in Canada who are diagnosed with a potentially fatal blood clot this year. You take the day off work to see a specialist. You sit down in the doctor’s office, in shock. You’ve never heard of venous thromboembolism before, and although you are prepared to find out about treatment, you didn’t predict that your doctor is about to tell you that your blood clot might be a symptom of something else: cancer. 

Fortunately, that’s a scenario that is quickly disappearing, thanks to the results of some practice-changing research at The Ottawa Hospital. Despite a longstanding belief that unexplained blood clots are linked with cancer, patients with venous thrombosis are no longer being subjected to cancer screening because it’s been proven they don’t need to be –unless it is routine and age-appropriate screening such as pap smears and prostate checks. 

This journey of discovery began when an Ottawa-area patient with an unexplained blood clot raised questions about the actual risk of cancer. 

“We had to say, well, we don’t really know,” says Dr. Carrier, a hematologist and senior scientist at The Ottawa Hospital. “And that led to the clinical trial.”

The clinical trial took place at nine sites across Canada and almost 900 patients with new diagnoses of venous blood clots participated. Half of the randomized group received standard cancer screening and the other received more extensive diagnostic screening using a CT scan.

There were a couple of surprising results, which have since been published in The New England Journal of Medicine. 

“We found the link that everybody thought was so big between venous thrombosis and cancer is not even as high as – or even close to – where we thought it was,” says Dr. Carrier, the lead author of the study and also an associate professor at the University of Ottawa. 

Only 3% of people with a venous blood clot had underlying cancer diagnosed over the following year, which is not far from rate of cancer in the general population. The results also proved that extensive screening also did not lead to the discovery of more cancers being diagnosed, or more cancers being missed. So unless patients have clear symptoms, there’s no point screening them for cancer anymore. No more screening means less anxiety for the patients, decreased radiation exposure, and a significant savings to the health care system.  Clinicians are also freed up for other tasks. 

The trial results offered a made-in-Ottawa answer to a common question, not only for thrombosis experts but also for general care doctors, internists, and medical professionals of all different levels, but it’s only one example of the practice-changing research that is happening at The Ottawa Hospital every single day.

“We are certainly uniquely positioned at The Ottawa Hospital; we have the research infrastructure,” says Dr. Carrier, who adds that the support for researchers is “phenomenal” at TOH in all sorts of different ways. “We see a lot of volume, so we have a good place to do research.”

Practice-changing research at The Ottawa Hospital is about more than just some lab results. “It’s really about the patient being an equal partner in the research process,” says Dr. Carrier. “So not only participating in clinical trials or clinical studies, but being part of the steering committee so to speak.”

Fundraising is currently underway for an expanded practice-changing research team and facilities at The Ottawa Hospital. As for venous thromboembolism: “We are struggling to create awareness,” says Dr. Carrier. “Creating awareness for venous disease is something that is close to my heart.” 

Dr. Carrier would also like patients to consider participating in research trials if the opportunity arises. After all, the advances in medical care have largely come about as a result of past clinical trials. 

“It’s an altruistic thing to do,” says Dr. Carrier. “And this is how we make patient care, better.” 



The Ottawa Hospital has more than 1,700 scientists, clinical investigators, graduate students, postdoctoral fellows and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease.  

- 30,000 Canadians are diagnosed with an unexplained blood clot in the legs or lungs every year.

- About 600 patients come to The Ottawa Hospital with blood clots in their lungs every year.

It’s estimated recent breakthrough research into blood clots and cancer will result in an annual savings of $9M in Canada alone.

This is the fourth part of an ongoing series about The Ottawa Hospital. Look for the evolving archive on