Clinical trials are done to make sure new treatments and procedures are safe and effective for people. For this reason, each new treatment and procedure is studied in several clinical trials. Each trial takes years to complete. For example, the BIG 1-98 trial, which compared Femara and tamoxifen after surgery to treat early-stage breast cancer, was started in 1998. The women took the medicines for 5 years and then were followed for several years after treatment, so the first results were available in 2005, 7 years after the trial began. In most cases, researchers like to have 5 to 10 years (or more) of follow-up data so they can be sure that any long-term side effects are discovered.