Cancer mortality trends in Canada: breast cancer, 1925-1982.

Breast cancer is the number one cause of death in Canadian women aged 20-74 years (for all 5-year age groups) and the second leading cause for those aged 75 years and over. To assess the long-term mortality of this disease, we collected and analyzed data from 1925 to 1982. A 3-year base period was used to obtain person-years exposure using Newton-Cotes' method. All rates were standardized to the 1956 Canadian population for age and sex using the direct method. Standard errors of age-standardized death rates (ASDR) were computed using Chiang's method. Mortality from breast cancer has been quite stable during the study period (at about 23.7 deaths/100,000 population). The lowest ASDR occurred in 1926 (at 17.5 deaths/100,000 population); the highest occurred in 1946 (when it reached 26.6 deaths/100,000 population). During 1951-1981, the ASDR fluctuated between 22.8 and 24.0 deaths/100,000 population. Examination of age sex-specific rates revealed a steady trend for 25-44-year-old females and a rise in mortality in the older age groups. It is suggested that part of this rise may be associated with changes in environment, life-style, and therapy.