Avastin Side Effects Linked to Increased Risk of Serious Blood Clots

A new report published in the Journal of the American Medical Association highlights the increased risk of blood clots associated with Avastin, a drug used to treat cancer. The researchers indicate that findings call for stronger warnings to be added to the drug’s label about the Avastin side effects.

Avastin (bevacizumab), which is marketed by Genentech and Roche, is a cancer drug that blocks tumor growth by preventing formation of new blood vessels which nourish the tumors. Avastin was approved in 2004 for treatment of lung and colon cancer, and it has been found to improve the survival rate when combined with chemotherapy.

According to the research reported by Dr. Shenhong Wu and his colleges at Stony Brook University Cancer center in New York, side effects of Avastin could increase the risk of developing vein blood clots by as much as one third.

The researchers evaluated data involving nearly 8,000 patients in 15 clinical trials and found that the percentage of people developing venous blood clots was 8.3% among Avastin users and 6.1% in the control group, for an increase in the relative risk of 33%.

The risk of Avastin blood clots was found to vary widely depending on the type of cancer involved, with 19.1% of those with colorectal cancer developing blood clots, 14.9% of non-small-cell lung cancer patients developing clots, 7.3% of breast cancer patients developing blood clots, but only 3% of kidney cancer patients treated with Avastin having blood clots.

According to Wu, a smaller study conducted in 2007 by Genentech, which involved 1,745 people, under estimated the blood clot risk with Avastin. Wu suggests that the Genentech study was too small and that his larger study was more significant and reliable.

Although the researchers indicate that the findings are not a reason for doctors to stop using the cancer drug, it is important for physicians and patients to be aware of the blood clot side effects of Avastin so that methods of preventing and treating blood clots can be reviewed.

The report suggests that information about the Avastin blood clot risk should be moved from its current location on the warning label into a prominently displayed “black box” warning, which would be the strongest warning which can be place on a prescription medication.