Doubts grew that Avastin wouldn't work, or that some serious side effect such as gastrointestinal bleeding would ground the once-promising drug.

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The major side effect observed with Xarelto is bleeding, similar to other anti-clotting drugs.

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Still, a press release from the National Institutes of Health said that life-threatening or fatal bleeding, mainly from the lungs, was the most common side effect, and was more common in patients receiving Avastin than just chemotherapy.

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