Mammography over the past 30 years, has resulted in over-diagnosis in roughly a third of cases. 30+% of women are unnecessarily treated for Breast Cancer

After excluding the transient excess incidence associated with hormone-replacement therapy and adjusting for trends in the incidence of breast cancer among women younger than 40 years of age, we estimated that breast cancer was overdiagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed.
STUDY: http://www.nejm.org/doi/full/10.1056/NEJMoa1206809