Randomized trials comparing surgical treatments of breast cancer show that radical mastectomy offers no greater benefit than simple mastectomy followed by radiotherapy. Furthermore, in terms of survival, radical mastectomy seems to be no better than wide excision followed by radiotherapy when the disease is clinically diagnosed as stage 1. The incidence of diagnosed breast cancer showed an 18% increase between 1935 and 1965 and a 50% increase between 1965 and 1975. However, breast cancer mortality has remained unchanged for at least the past 40 years. Analysis of survival curves of women with breast cancer suggests that two or more populations exist, with about 40% suffering fatal outcome unaffected by treatment. The remaining 60% exhibit a relative mortality only modestly different from that of women of similar ages without evidence of disease. Increasing detection of an entity that is histologically defined as malignant but biologically relatively benign could account for the observed increase in incidence.