Trends in breast cancer incidence in Sweden 1958-1988 by time period and birth cohort

Abstract

Summary Statistics from the Swedish National Cancer Registry based on all 110,658 cases of invasive breast cancer during the 31-year period were analysed. Age-specific incidence rates increased over successive calendar periods. The average annual increase in the age-standardised incidence rate was 1.3%, with the greatest percentage changes among the youngest age groups. During the latter half of the study period, the rates of increase tended to diminish in the youngest age groups and even reversed significantly among women from 75 years of age. In analyses using age-period-cohort models, the best fit of the cancer incidence data was found for the full model which simultaneously considered the effects of age, period and cohort. Cohort effects were found to be more important than period effects, in terms of model fit. These effects emerged as a seemingly consistent, and in a logarithmic scale, fairly linear increase in the relative risk of breast cancer incidence with a 3-fold elevation in women born in the 1950's relative to those born in the 1880's It is concluded that the rising breast cancer incidence in Sweden is explained chiefly by birth cohort effects, which indicate persistent secular changes in largely unknown risk factors associated with life style. We could not in the present data see any clear evidence for an adverse effect of contraceptive or replacement sex steroids on breast cancer incidence.

Recent trends in breast cancer incidence in Sweden

“…Both in Scandinavia (Ewertz and Carstensen, 1988;Persson et al, 1993) (Chu et al, 1996). In a previous analysis of nation-based breast cancer incidence rates in Sweden during 1958-88, we found an average annual increase in the agestandardized rates of 1.3% (Persson et al, 1993). Although present in all age groups, this increase was most rapid among younger women.…”

“…A recent analysis of breast cancer incidence from the Surveillance Epidemiology and End Results Program (SEER) in the USA during the period 1989-93 demonstrated among women aged 40 years and older a pronounced increase for in situ and localized tumours but a drop for regional cancers, a pattern probably due to the introduction of mammography screening (Chu et al, 1996). In a previous analysis of nation-based breast cancer incidence rates in Sweden during 1958-88, we found an average annual increase in the agestandardized rates of 1.3% (Persson et al, 1993). Although present in all age groups, this increase was most rapid among younger women.…”

“…Keywords: breast cancer; incidence; trends The occurrence of breast cancer has been increasing worldwide in high-incidence Western countries as well as in low-incidence Asian countries (Quinn and Allen, 1995). Both in Scandinavia (Ewertz and Carstensen, 1988;Persson et al, 1993) (Chu et al, 1996). In a previous analysis of nation-based breast cancer incidence rates in Sweden during 1958-88, we found an average annual increase in the agestandardized rates of 1.3% (Persson et al, 1993).…”

“…Both in Scandinavia (Ewertz and Carstensen, 1988;Persson et al, 1993) and in the USA (Holford et al, 1991), secular trends were linked to birth cohorts, indicating that exposure to important (but not well-characterized) risk factors has changed over generations. A recent analysis of breast cancer incidence from the Surveillance Epidemiology and End Results Program (SEER) in the USA during the period 1989-93 demonstrated among women aged 40 years and older a pronounced increase for in situ and localized tumours but a drop for regional cancers, a pattern probably due to the introduction of mammography screening (Chu et al, 1996).…”

Trends in breast cancer incidence in Hong Kong between 1973 and 1999: an age-period-cohort analysis

“…One strategy to solving the nonidentifiability problem is to assume the regression coefficients of the first and last periods to be zero, a technique commonly used in several previous studies (Tarone and Chu, 1996;Shahpar and Li, 1999). With this assumption, it was possible to obtain firstorder relative risk estimates and associated 95% confidence intervals for the cohort effects (Holford, 1991;Persson et al, 1993). Similarly, relative risks for period effects were generated by imposing constraints such that the regression coefficients of the first and last cohorts were assumed to be zero.…”