The era of technical and scientific progress ushered in with the twentieth century brought new medical knowledge such as the Halstead 'radical' mastectomy, which promised a cure for breast cancer. These advances in medical knowledge were premised on an epidemiological model of disease, which shaped the treatment and public understanding of breast cancer through most of the twentieth century--to be replaced by a systemic model of breast cancer in the later years of the century. This article traces how this shift was both influenced by and influential on public understandings of medicine and disease. The author argues that, while the epidemiological model of disease shaped treatment options and public health campaigns through most of the century, current treatment regimes and health campaigns are shifting to reflect changes in the underlying model of disease (toward a systemic model).