The surprising decision by US regulators to give the green light to Genentech’s blockbuster Avastin as a treatment for breast cancer has both delighted and outraged observers.

The US Food and Drug Administration has granted accelerated approval for Avastin (bevacizumab), in combination with paclitaxel, as a treatment for patients who have not received chemotherapy for their metastatic HER2-negative breast cancer. The move has stunned many people given that the agency has not acted on the recommendation of one of its advisory panel, which last December voted 5-4 against the drug, saying Avastin’s effectiveness in slowing the progression of breast cancer did not outweigh its toxic side effects.

The approval is based on a Phase III study (E2100) that showed that Avastin in combination with paclitaxel resulted in a 52% reduction in the risk of disease progression or death compared to those treated with paclitaxel alone and a doubling in progression-free survival. The go-ahead falls under the FDA's accelerated approval programme, which allows the agency to clear products for life-threatening diseases based on initial positive clinical data.

Genentech said that it has shared with the FDA a summary of the results from a second Phase III trial, AVADO (with docetaxel) and is expecting data from a third late-stage trial (RIBBON I) in first-line metastatic breast cancer in late 2008. A full review of both of these will be required for this latest to be converted into a full approval.

"There is no cure for metastatic breast cancer so it is important to control the disease as early and for as long as possible," said Kathy Miller of the Indiana University School of Medicine and lead investigator on the E2100 trial. "Now with Avastin plus paclitaxel, we can increase the time a woman's cancer is kept under control, and offer a biologic option to women who previously were limited to chemotherapies alone."

However the fact that approval for Avastin in this indication (it is already very successfully marketed for colorectal and lung cancer) has been granted because it shrink tumours and not because its extends survival has sparked off a major debate. Barbara Brenner, executive director of the US activist group Breast Cancer Action, said the studies failed to show that Avastin increases the long-term survival or quality of life for women with advanced disease. The agency “has lowered the bar under pressure from the industry at a time when the FDA is under enormous pressure around its drug approvals," she said.

However Richard Pazdur, head of oncologic drugs at the FDA's Center for Drug Evaluation and Research, expressed the importance of having “regulatory flexibility” to approve effective treatments where there is not overall survival. He said the agency had sympathy for the view that delaying the progression of life-threatening disease “may be a direct clinical benefit in itself”.

He added, however, that the decision did not represent a change in the FDA’s policies and it still sees overall survival as the gold standard for cancer drugs. One clear winner in this case, however, is Genentech and the approval in the new indication could be worth up to $1.8 billion at peak sales. Avastin is already approved for patients with breast cancer in the European Union, where it is marketed by Genentech’s majority owner Roche.