A Pfizer drug, exemestane, reduced the risk of breast cancer in women by more than one-half by blocking the hormone estrogen, Boston researchers say. Dr. Paul E. Goss, director of the breast cancer research program at Massachusetts General Hospital, says the trial tracked 4,560 postmenopausal women from the United States, Canada, Spain and France who had at least one risk factor for breast cancer age 60 or older or having a breast biopsy indicated higher risk, The Boston Globe reported. One group of women received the drug already approved to treat breast cancer and the other group received a placebo. All were tracked for seven years. \"There was a 65 percent reduction in the risk of breast cancer a pill that can do that to the commonest cancer that affects women globally and kills women globally; there\'s no such pill that I know of for any kind of cancer,\" Goss, the study\'s lead author, told the meeting of the American Society of Clinical Oncology in Chicago. \"We haven\'t seen any serious toxicity that might stifle someone\'s decision to try and take this drug.\" The findings, also published in the New England Journal of Medicine, said the women taking exemestane had more side effects including hot flashes, fatigue, sweating and insomnia than those on the placebo, but the rate of bone fractures, osteoporosis and cardiovascular effects was the same in both groups.