Genentech's blockbuster cancer drug Avastin raises blood clot risk

New York, November 19: A new American study has found that Genentech's blockbuster cancerdefine drug Avastin raises the risk of blood clots in leg or lung veins by 33 percent, when combined with chemotherapy.

It has been known that use of Avastin causes blood clots in arteries but scientists didn’t know whether it resulted in similar problems in veins, a condition known as venous thromboembolism (VTE).

Lead author of the study, Dr. Shenhong Wu, MD, PhD of Stony Brook University Cancerdefine Center in New York, U.S., said that the study shows “a significant increased risk with Avastin for patients while they are taking chemotherapy."

The latest analysis of 15 clinical trials, which appears in the Nov. 19 issue of the Journal of the American Medical Association, involving a total of almost 8,000 patients with different types of advanced solid tumors found that Avastin (marketed by Genentech and Roche) increases the risk of a blood clot in the veins from about 10 percent to 13 percent of the patients.

Subjects who took Avastin had a 33 percent higher risk of developing blood clots as compared to controls. The risk was higher regardless of whether a person is taking a low dose or a high dose of Avastin.

Dr. Alok Khorana, an associate professor of medicine at the University of Rochester Medical Center, said, "They were able to expand the sample size, and it looks like a significant increase in venous blood clots."

"Even though the event rate is not that high, it's still high enough that we need to exercise caution in using the drug. Patients need to be aware of the symptoms of blood clots -- swelling in the leg, sudden chest pain, shortness of breath -- and physicians need to be aware," he added.

Kristina Becker, a spokeswoman for drug company Genentech, said Avastin's label already carries a warning about blood clots in the arteries.

If blood clots form in a veindefine it limits blood flow which in turn causes swelling, tenderness and pain. The blood clots can be fatal when they become dislodged and travel to the lungs or other areas, causing strokes, severe organ damage or even death. Many people suffering from cancer have an increased risk of VTE, where clots can break off and travel through the bloodstream, potentially blocking blood flow to the lungs.

Researchers say that the results should not dissuade cancer patients from taking the drug; instead both patients and doctors just need to be on the lookout for blood clots.

Avastin, known generically as bevacizumab, is a monoclonal antibody which aims VEGF, a molecule essential for the growth of new blood vessels. It starves tumor cells by preventing them from forming new blood supplies. But blocking VEGF also perks up chances of blood clotting. Avastin is given to patients suffering from a number of cancers such as breast, lung, colorectal and kidney cancer.

Another past study, though, had found that widely used cancer drug, Avastin, slows the progression of a common type of advanced breast cancer (HER2-negative form) when teamed with a chemotherapy drug.