CT scanning adds little in search for cancer after embolism

By Gene Emery

NEW YORK (Reuters Health) - Adding CT scanning to the workup for cancer following an unprovoked venous thromboembolism does little to increase the likelihood that a tumor will be found, Canadian researchers reported Monday at the International Society on Thrombosis and Haemostasis 2015 Congress in Toronto.

The findings, also reported online by the New England Journal of Medicine, show that the overall risk of discovering a cancer is low - less than 5%.

"Our results suggest that a limited screen strategy for occult cancer (history taking, physical examination, basic blood testing, chest radiography, and age-specific and sex-specific cancer screening) may be adequate for patients who have a first unprovoked venous thromboembolism," the researchers wrote in their Journal article.

Since a link between unexplained thromboembolism and cancer was first described in the 1800s, generations of doctors have been looking for malignancy following a leg or lung clot "without having too much data to show that it's actually a good thing to do," chief author Dr. Marc Carrier of the Ottawa Hospital told Reuters Health in a telephone interview.

Such a search isn't unreasonable. "If you look at all the diagnoses of venous thrombosis, about 20 to 25% will happen in cancer patients because cancer makes your blood very prone to clots," he said.

The new study, the largest conducted on the question, was an attempt to determine how aggressive such screening needs to be.

It focused on 854 people treated in nine Canadian medical centers whose clots didn't have an obvious cause and who did not have a history of unprovoked venous thromboembolism. Such clots affect roughly 250,000 people in the U.S. and Canada each year.

In the group that received basic screening such a blood work, a chest X-ray, and tests for breast, cervical and prostate cancer, 3.2% were diagnosed with cancer within a year.

Among the remaining volunteers, who received a CT scan of the abdomen and pelvis in addition to the other cancer screening, tumors were found in 4.5% during that first year (P=0.28).

Based on other studies, the researchers had expected to see more tumors - perhaps cancers in as many as 10% of patients, Dr. Carrier said.

Other measures also failed to show a benefit for CT screening.

Among all the cancers found within a year after randomization, 29% were discovered after the volunteers had been deemed cancer-free by limited screening. The rate was 26% in the CT scanning group (P=1.0).

"Acute leukemia (2 cases), gynecologic tumors (2), and colorectal tumors (2) were the most frequent cancers missed by the screening strategies, with no significant differences between the two strategies," the researchers reported.

When a tumor did appear, it typically took 4.2 months to be diagnosed in the limited screening group and 4.0 months in the CT scanning group (P=0.75).

CT scanning did not affect mortality.

Such scans cost about $300 in Canada.

Showing that CT scanning doesn't really improve the likelihood of finding a tumor "is going to save some health care dollars but more importantly" it could save lives because CT scanning itself increases the risk of cancer, Dr. Carrier said.

SOURCE: http://bit.ly/1GgK7Yv

N Engl J Med 2015.

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