Despite the appeal of early detection of breast cancer, uncertainty about the value of mammography continues.1 In this issue of the Archives, Zahl et al2 use a clever study design in an attempt to estimate the value of screening. The initiation of a public screening program in Norway allowed them to compare biopsy-confirmed invasive tumors in women receiving a single mammogram between the ages of 50 and 64 years, with the cumulative number of tumors in a group of women aged 50 to 64 years who had been screened on 3 occasions. Because a variety of risk factors were similar for the 2 groups, the cumulative tumor rate in the multiple screen group was expected to be the same as the rate in the age-matched single screen group. However, the rate in the single screen group was about 22% lower.
Kaplan RM, Porzsolt F. The Natural History of Breast Cancer. Arch Intern Med. 2008;168(21):2302-2303. doi:10.1001/archinte.168.21.2302