Testing ‘Clemmensen’s hook’ in the death rate from breast cancer

Breast cancer is the most common form of cancer among women. Since 1945 the number of cases has almost doubled. However, since 1990 the survival rate has improved significantly. The literature discusses models of the age distribution of breast cancer mortality developed on the basis of a two-disease theory of breast cancer incidence called Clemmensen’s hook. On the basis of Danish data on the death rate from breast cancer the existence of Clemmensen’s hook is discussed critically. A model encompassing five discussed studies on the subject is developed. When the cohort effects are included in the model, the two-disease theory for breast cancer disappears. The paper concludes that Clemmensen’s hook does not exist as the overlapping of two curves corresponding to pre- and post-menopausal tumors for breast cancer, respectively.