ABSTRACT
The Canadian National Breast Screening Study (CNBSS) included two individually randomized controlled trials of breast screening to evaluate the efficacy of screening. The goal of screening is to achieve sufficiently early detection of a disease, such as breast cancer, so that deaths are prevented. The CNBSS began screening women aged 40–59 in January 1980. This chapter discusses the CNBSS in the context of criticisms pertaining to randomization, mammography (MA), "contamination", and results, with reference to other screening trials. It reviews the mortality paradox wherein screened women aged 40–49 are more likely to die of breast cancer in the first years after screening is initiated compared to unscreened control women. The chapter examines whether women who currently seek MA screening are completely informed and, if not, why not. It speculates on the nature of the breast screening controversy.
