根据以下材料，回答题 Cancer Drug Trials Often Halted Early An increasing number of clinical trials for new cancer treatments are being halted before the risks and benefits have been fully evaluated， say Italian researchers， who warn that this growing trend could put patients at risk of harm from new therapies rushed into use. The researchers looked at 25 randomized， controlled clinical trials that were stopped early because the treatments had started to show benefit to patients. 'When we analyzed 25 trials over a 10-year period between 1997 and 2007， we found a consistent increase in prematurely stopped trials——more than 50 percent were stopped within the last three years，' study co-author Giovanni Apolone said at a news conference Tuesday. Of 14 trials halted early and published between 2005 and 2007， the researchers found that 11（79 percent） of them were used to support drug approval applications submitted to the European Medicines Agency and the U.S. Food and Drug Administration. 'This suggests a strong commercial component in stopping trials prematurely. In fact， this strategy could guarantee quicker access to the market for companies. On the other hand， a quicker clinical drug development may lead to an 'immature' benefit/risk balance of new drugs，'Apolone said. He and his colleagues 'are aware that trials stopped early because they are showing benefit may result in identification of promising new treatments for patients. However， findings obtained following this strategy should be considered to be preliminary results that require subsequent confmnation.' It can take several years for the long-term benefits or harmful side effects of a new treatment to become apparent， Apolone noted， but the average duration （持续时间） of the 25 studies he and his colleagues analyzed was 30 months， with a range from 12 to 64 months. They also found that at the time five of the studies were stopped， they'd enrolled less than 40 percent of the total number of patients planned for final analysis. 'Clinical trials need to stop early for superior benefit whenever there's proof beyond reasonable doubt that the new treatment really is superior. That would be an ethical obligation，'Stuart Pocock， a professor of medical statistics at the London School of Hygiene and Tropical Medicine in the United Kingdom， said at the news conference. 'However， too many trials are stopped early claiming efficacy （功效） without strong evidence being available.' The number of prematurely stopped clinical trials has increased recently. 查看材料