The biotech’s blockbuster cancer med is linked to a significantly increased risk of blood clots in the veins, according to a meta-analysis in the Journal of the American Medical Association. Genentech, however, quickly challenged the findings and denied the need to update the Avastin labeling.
The review found that the risk of blood clots was 33 percent higher among patients on Avastin compared with control group subjects in 15 clinical trials analyzed. The findings contradict conclusions from a pooled analysis of five studies by Genentech researchers, who reported last year that clots did not rise significantly among subjects on Avastin, The San Francisco Chronicle writes.
Avastin, which is jointly marketed by Genentech and Roche, is designed to block tumor growth by preventing blood vessels from forming to nourish them, the Chron continues, noting that the drug is also associated with serious side effects, including blood clots in the arteries. Other dangers, including hemorrhage and perforations of the bowel, are detailed in a Black Box warning on the Avastin label.
The JAMA researchers suggest the risk of blood clots originating in the veins might belong in the warning, and Shenhong Wu, an oncologist at the Stony Brook University Cancer Center in Stony Brook, NNew York, says Genentech’s review of five studies underestimated the problem.
According to Wu, the 1,745 subjects in Genentech’s pooled analysis weren’t enough to deect a statistically significant risk. His analysis evaluated 7,956 subjects in 15 trials. The percentage of people developing vein clots was not high in either the Avastin-treated group, where it was about 8.3 percent, or the control group, where it was about 6.1 percent. But by comparing those two numbers, Wu’s team found an increase in relative risk with Avastin of 33 percent.
Philippe Bishop, Genentech’s head of clinical development for Avastin, tells the Chron that the results of Wu’s analysis may have been skewed by several factors, such as different methods of reporting data in each of the 15 trials. But Bishop acknowledged that studies in general have found an incidence of venous clots averaging about two to three percentage points higher among those on Avastin compared with control groups.
Such info is included in Avastin’s label, but he disputes that the data reveal a statistically significant difference in risk of 33 percent. No change in the drug’s label is needed, according to Bishop. “I think our label reflects the way Avastin should be used,” he tells the Chron.
Whether Avastin itself is behind the higher incidence of vein clots seen in many studies is still an open question, and finding an answer would require another large trial, both Wu and Bishop agree. Such a trial would be designed to identify other potential causes, such as additional treatments given more frequently to those on Avastin, for example, the Chron writes.
Gary Lyman, a Duke University professor medicine who helped develop physician guidelines for protecting cancer patients from blood clots in the veins, says Wu’s paper may make people more aware of the risks. But it may not change medical practice much. “It’s just reinforcing what we’ve suspected,” he tells the Chron.
Genentech Disputes Avastin And Blood Clot Risk
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