Genentech's bevacizumab (Avastin) received approval from US drug regulators for the treatment of recurring brain tumors called glioblastoma, or GBM, after promising results from several clinical trials.
However, a randomized trial of 637 patients found no difference in survival rates between those who took the drug to supplement their chemotherapy and those who took a placebo.
"Unless we can identify a group of patients that clearly benefits from early use of bevacizumab, it appears that it should not be used in the first-line setting," said Mark Gilbert, a professor of neuro-oncology at the University of Texas MD Anderson Cancer Center in Houston.
"Bevacizumab remains an important part of our armory against glioblastoma, but in most situations it should be reserved as a salvage regimen."
While the patients who received the drug also showed more side effects -- particularly low platelet counts, blood clots and high blood pressure -- Gilbert said the increased toxicity would be acceptable if a survival benefit had been found.
The phase III trial also concluded that the drug had a detrimental impact on quality of life, with patients showing a greater degree of cognitive decline.
GBM is the most common malignant brain tumor in adults, and few patients live more than five years after their diagnosis. The average survival rate for those in clinical trials is less than 16 months.
Patients were unblinded after their tumors came back to allow for treatment with or without bevacizumab.
"The cross-over component allowed comparison of risk and benefit of early versus late treatment," Gilbert said. "We now know by giving it late you delay the risk of toxicity, and that may be relevant."
An estimated 14,080 people will die from brain tumors in the United States this year and 23,130 new cases will be detected.
The study was presented at the annual meeting of the American Society of Clinical Oncology in Chicago.