Avastin Plus Chemo May Raise Clot Risk

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There was no statistically significant difference in the incidence of blood clots in the veins between the two groups.

People who had had previous clots and who were 65 or older were at especially heightened risk, the team found.

"If the patients are over 65 with a history of arterial thrombosis, you have to be more cautious, because it looks like the risks are greater," said Astrow.

Based on the findings, "It's important for physicians to consider two things," Lang said. "One is the Avastin survival benefit both in colorectal cancer and in lung cancer, but also the risk profile in making treatment decisions."

Although it's still unclear what might be causing this association, the researchers speculated that VEGF (vascular endothelial growth factor), a natural compound that promotes the growth of blood vessels, might be implicated.

Avastin, an anti-angiogenesis drug, works by inhibiting VEGF, in essence blocking blood supply to the tumor.

There is some evidence that anti-VEGF therapy might cause blood clots, the researchers noted.

More information

The National Cancer Institute has more on targeted cancer therapies.