The government revoked the approval of breast cancer drug Avastin last week, citing dangerous side effects and a lack of evidence that it prolongs life. FDA Commissioner Margaret Hamburg said it was a “difficult decision,” referencing the patients who have been lobbying to keep the drug. But, she added that “it is clear that women who take Avastin for metastatic breast cancer risk potentially life-threatening side effects without proof that the use of Avastin will provide a benefit, in terms …