US drug regulators have rescinded approval of a breast cancer drug, saying it is not effective enough to justify the risks of taking it.The drug, Avastin, was approved for US use in 2008, but UK officials have also rejected claims that it prolongs life.Further research showed it did not help patients live longer or improve quality of life, Food and Drug Administration commissioner Margaret Hamburg said.Avastin will still be used to treat other kinds of cancer.The drug is used to treat breast cancer that has spread to other parts of the body. It works by starving cancer cells of a blood supply.However, its side-effects include severe high blood pressure, massive bleeding, heart attack or heart failure and tears in the stomach and intestines, FDA studies have found.FDA approval of the drug had initially been given under a special programme that allows patients to start using promising treatments while the manufacturer finishes the studies to prove the medicine works as well as expected.The decision to withdraw the approval - which can happen if results of the research do not match predictions - was not easy, the FDA said.Stalling cancer growth"With so much at stake, patients and their doctors count on the FDA to ensure the drugs they use have been shown to be safe and effective for their intended use. Sometimes, the results of rigorous testing can be disappointing," Ms Hamburg told the Associated Press news agency.US health insurance companies could remove the drug, which can cost as much as $100,000 (£63,342) per year, from their coverage - although doctors would still be permitted to administer the drug.But the government-backed Medicaid programme has said it has no immediate plans to change its policy of paying for it.Some advocates of the drug disagree with the watchdog's decision."The bottom line is that they are throwing out the baby with the bathwater. There absolutely may be subsets of carefully chosen breast cancer patients who benefit from Avastin," said Dr Elisa Port, co-director of the Dubin Breast Center of Mount Sinai Hospital in New York.Roche, the Swiss manufacturer of the drug, has said it will undertake further study of the treatment, especially with the chemotherapy drug paclitaxel, to try to identify which patients might be best suited to benefit from use of the drug.The company says it expects the medicine will generate $7.6bn (£4.8bn) of revenue annually, despite the FDA decision.The drug was approved on the basis of a study that showed Avastin was able to stall the growth of breast cancer by five-and-a-half months, when used together with a standard chemotherapy treatment.But subsequent studies revised the period of delay to between one and three months, and there was no evidence to show that the drug extended patients' lives.International problemsThe US decision comes after Avastin fell foul of health authorities in the UK and in Europe.In February 2011, the UK's National Institute for Health and Clinical Excellence (NICE), the NHS drugs advisory body, said Avastin should not be used to treat secondary breast cancers.NICE, which issues guidance for NHS in England and Wales, said there was insufficient evidence that the drug prolonged life.This guidance followed a recommendation by the European Medicines Agency (EMA) that doctors only prescribe the drug in combination with the taxane drug, paclitaxel.