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Just as the drug blocks new blood vessels that nourish tumors, it may also block new vessels that help the body heal and keep tissues strong. The findings highlight the importance of monitoring patients on Avastin for bleeding and other warning signs.

Experts have called on Genentech to do research to sort out which patients are most likely to benefit or be harmed by Avastin.

“That’s an important part of clinical research,” said Dr. Daniel Hayes, clinical director of the breast cancer program at the University of Michigan. Hayes wrote an accompanying editorial in the journal but wasn’t involved in the analysis.

Avastin’s enormous costs also must be considered, he said. The drug is dripped into a vein and must be given in a medical office or hospital.

“This drug is as expensive as any therapy we’ve ever had in cancer,” he said. “We can’t afford to give a drug to everybody when it helps only a portion of those to whom it is given.”

Roche reported Avastin sales of nearly $6 billion in 2009.

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Online:

JAMA: http://jama.ama-assn.org