The increasing incidence of breast cancer in Alberta 1953-1973

The incidence of female breast cancer in Alberta increased steadily by one case per 100,000 per year from 1953 to 1973 to a current rate of 68.6 per year when adjusted to the 1950 U.S. population. Incidence rates of breast cancer in Alberta and Saskatchewan were identical after population adjustment. The incidence increased in women over 40, implicating an increase in the postmenopausal type of breast cancer. Birth cohort analysis showed increased age-specific incidence rates in middle-aged women occurring in successive cohorts from 1903 to 1918, a result similar to that found in Saskatchewan, Connecticut, and Finland. The menopausal hook is disappearing in Alberta data, apparently due to cohort-specific increases in incidence. Possible etiological factors involved in these incidence changes are discussed; a detailed analysis of specific etiological factors is currently underway on over 3,000 patients with malignant or benign breast disease who were examined at the Dr. W. W. Cross Cancer Institute in Edmonton from 1971 to 1974.