By reviewing Medicare claims following mammographic screening in 23,172 women older than 65 years, one study  found that, per 1,000 women, 85 had follow-up testing, 23 had biopsies, and 7 had cancer. Thus, the PPV for an abnormal mammogram was 8%. For women older than 70 years, the PPV was 14%.
An audit of mammograms performed in 1998 at a single institution revealed that 14.7% of examinations resulted in a recommendation for additional testing (Breast Imaging Reporting and Data System category 0), 1.8% resulted in a recommendation for biopsy (categories 4 and 5), and 5.7% resulted in a recommendation for short-term interval mammography (category 3). Cancer was diagnosed in 0.5% of the cases referred for additional testing. 
Overdiagnosed disease is a neoplasm that would never become clinically apparent without screening before a patient's death. The prevalence of cancer in women who died of noncancer causes is surprisingly high. In an overview of seven autopsy studies, the median prevalence of occult invasive breast cancer was 1.3% (range, 0%–1.8%) and of ductal carcinoma in situ was 8.9% (range, 0%–14.7%).[6,7] A "perfect" screening test would identify approximately 10% of "normal" women as having breast cancer, even though most of those cancers would probably not result in illness or death. Treatment of these cancers would constitute overtreatment.
Currently, cancers that will cause illness and/or death cannot be confidently distinguished from those that will remain occult, so all cancers are treated.
To determine the number of screen-detected cancers that are overdiagnosed, one can compare breast cancer incidence over time in a screened population with that of an unscreened population.
Population-based studies could demonstrate the extent of overdiagnosis if the screened and nonscreened populations were the same except for screening. Unfortunately, the populations may differ in time, geography, culture, and the use of postmenopausal hormone therapy. Investigators also differ in their calculation of overdiagnosis as they adjust for characteristics such as lead-time bias.[8,9] As a consequence, the magnitude of overdiagnosis due to mammographic screening is controversial, with estimates ranging from 0% to 54%.[8,9,10,11]
Several observational population-based comparisons consider breast cancer incidence before and after adoption of screening.[12,13,14,15,16] If there were no overdiagnosis—and other aspects of screening were unchanged—there would be a rise in incidence followed by a decrease to below the prescreening level, and the cumulative incidence would be similar. Such results have not been observed. Breast cancer incidence rates increase at the initiation of screening without a compensatory drop in later years. One study in 11 rural Swedish counties showed a persistent increase in breast cancer incidence following the advent of screening. A population-based study showed increases in invasive breast cancer incidence of 54% in Norway and 45% in Sweden in women aged 50 to 69 years, following the introduction of nationwide screening programs. No corresponding decline in incidence in women older than 69 years was ever seen. Similar findings suggestive of overdiagnosis have been reported from the United Kingdom  and the United States.[15,16]