February 13 (HealthDay News) -- The blood thinner warfarin does not reduce catheter-related blood clots in cancer patients, so new treatments are needed to prevent this complication, says a U.K. study.

About 50 percent of cancer patients develop venous thromboembolism, which can be caused by a number of factors, including the use of central venous catheters to deliver infusional chemotherapy, according to background information in the study. The use of warfarin with the catheters to prevent clotting is controversial because there's no clear evidence that it's effective.

The study included 1,590 cancer patients at 68 centers who were receiving chemotherapy through central venous catheters. The patients were randomly selected to receive either no warfarin, a fixed dose of 1 milligram of warfarin a day or dose-adjusted warfarin daily.

Overall, rates of catheter-related blood clots were the same (6 percent) whether people were or were not given warfarin. Those who received dose-adjusted warfarin did have fewer blood clots than those given the fixed dose (3 percent vs. 7 percent), but there were more occurrences of major bleeding in the dose-adjusted group (16 vs. 7).

The study was published in this week's edition of The Lancet.

"The rate of symptomatic catheter-related thromboses reported in clinical trials has fallen substantially over the past decade," wrote Annie Young and colleagues from the Institute for Cancer Studies at the University of Birmingham. "The improvements in catheter technology, placement and aftercare are contributing to this reduction. When any benefit of thromboprophylaxis (treatment to prevent blood clots) was balanced against the risk of major bleeding, the combined outcome showed no advantage with the use of any dose of warfarin."

"These findings only add to the assertion that the time has come to move on from warfarin for thromboprophylaxis in patients with cancer," they wrote. "We should consider new treatments."

Dr. Paolo Prandoni, of the University of Padua in Italy, wrote in an accompanying editorial that though there's no evidence that warfarin helps prevent catheter-related blood clots in cancer patients, doctors should make an effort to identify people at highest risk of clotting because they might benefit most from anti-clotting treatment.

SOURCE: The Lancet, news release, Feb. 12, 2009