A group of investigators sought to document the incidence of breast cancer within a year following a negative screening mammographic examination. Among approximately 200,000 women who took part in a screening program in a U.S. metropolitan area during the 1990s, they identified those who were diagnosed with breast cancer (and whose cancer was reported to a population based cancer registry serving that area) during the 12 months following each woman’s last negative exam. (There was an average of 2.0 screening mammograms per woman during the period of the study.)

The observed incidence of breast cancer was 29.5 per 10,000 during the year following the most recent negative exam.