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Avastin Plus Chemo May Raise Clot Risk

But the cancer drug's benefits may still outweigh the risk, experts say

WEDNESDAY, Aug. 8, 2007 (HealthDay News) -- Treating cancer patients with the cancer drug Avastin in conjunction with chemotherapy boosts their risk of blood clots in arteries compared to giving chemotherapy alone, a new study finds.

The risk of blood clots in veins was not increased with the combination therapy, said researchers in the Aug. 7 issue of the Journal of the National Cancer Institute.

"The events in this study have been characterized in the Avastin label, which already includes a warning about the potential risk for arterial thrombosis [blood clots in the arteries]," noted Edward Lang, a spokesman for Genentech, which makes Avastin and conducted this study. "This is not new information. Basically, this shows that results from this study are consistent with the interpretation that is already on the label."

"I don't see this changing anyone's treatment," added Dr. Alan Astrow, director of hematology/oncology at Maimonides Cancer Center in New York City. "These are non-trivial complications, but, in the setting of metastatic lung cancer or colon cancer and probably breast cancer, the drug is clearly beneficial," said Astrow, who was not involved in the study.

Previous studies had shown that Avastin (bevacizumab) improves survival for patients with metastatic colorectal and non-small-cell lung cancer when added to traditional chemotherapy and used as a first-line treatment. The combination also improved survival when used in people with previously treated metastatic cancer of various kinds.

But previous trials had also found an increased risk of arterial blood clots in patients with metastatic colorectal cancer who were taking Avastin.

Here, researchers analyzed pooled data from five randomized controlled trials that included, all told, 1,745 patients with metastatic colorectal, breast, or non-small cell lung cancer.

Among patients who received the combination therapy, 3.8 percent experienced blood clots in their arteries, compared with 1.7 percent of those on chemotherapy alone.

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.

SOURCES: Edward Lang, spokesman, Genentech, South San Francisco; Alan Astrow, M.D., director of hematology/oncology, Maimonides Cancer Center, New York City; Aug. 7, 2007, Journal of the National Cancer Institute
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