It is estimated that 25-50% of men may be over-treated for their prostate cancer. This means they undergo treatments that incur adverse effects (e.g. erectile dysfunction, incontinence) for a cancer that is not likely to spread during their lifetime. Active surveillance is an alternative option for patients when the prostate biopsy indicates their cancer is unlikely to spread quickly. However, in as many as 30 percent of cases, the cancer may turn out to be more aggressive than it initially appeared at the time of diagnosis.