Unprovoked venous thromboembolism may be one of the earliest signs of cancer, with a number of patients going on to receive a diagnosis of cancer in the following year. However, a recent Canadian study found no clinically significant benefit from adding CT to routine screening of venous thromboembolism patients.

Results of the trial were published June 22 in the New England Journal of Medicine.

Up to 10 percent of patients with unprovoked venous thromboembolism are diagnosed with cancer in the following year, while 60 percent of occult cancers are diagnosed shortly after an unprovoked venous thromboembolism diagnosis, according to authors Marc Carrier, MD, of the Ottawa Hospital Research Institute at the University of Ottawa, and colleagues.

“Faced with these troubling statistics, clinicians, patients, and policymakers struggle with how aggressive to be in screening for occult cancers in patients who present with unprovoked venous thromboembolism,” they wrote, noting there is great variation in practice regarding screening.

Carrier and colleagues sought to compare limited occult-cancer screening (featuring basic blood testing, chest x-ray and screening for breast, cervical and prostate cancer), with a combination of limited screening and CT.

A total of 854 patients were included in the study, and 33 (3.9 percent) received a new diagnosis of occult cancer during one-year follow up. The limited screening group featured 431 patients, of whom 14 were later diagnosed with cancer, and the CT group featured 423 patients, of whom 19 were diagnosed with cancer.

Four of the occult cancers (29 percent) were missed with the limited screening strategy, while five (26 percent) were missed by the strategy that included limited screening plus CT. The authors reported no significant difference between groups in mean time to cancer diagnosis or cancer-related mortality.

They added that even looking at the lower boundary of the confidence interval, meaning the best-case scenario, the addition of CT would miss fewer cancers than limited screening alone by a margin of 1.12 percentage points. Under this best-case scenario, it would take 91 screenings to detect one missed occult cancer.

“Hence, it is exceedingly unlikely that CT permits early detection of clinically relevant numbers of cancers and even less likely that early detection of these cancers would provide an overall net clinical benefit,” wrote Carrier and colleagues.

The authors did note that the rate of occult cancer detection in their study was lower than expected, with previous estimates showing the rate as high as 10 percent in the year following diagnosis of unprovoked venous thromboembolism. More recent research, however, has hinted at a lower risk, however, possibility due to better cancer screening overall.