Epidemiology of breast cancer in Japan.

Background: A recent increase in the numbers of deaths and incident cases of breast cancer among Japanese women stimulated the authors to summarize the trends in female breast cancer mortality and incidence rates in Japan.

Methods: The number of deaths from female breast cancer was obtained from the national vital statistics. Estimated incidence rates, based on several cancer registries, were also used for the analyses. The trends in the age-adjusted and age-specific rates were examined. Age and birth cohort effects on the incidence and mortality rates were examined, using multiplicative models.

Results: The age-adjusted mortality rate has been increasing since the 1960s (4.1 per 100,000 population in 1950 and 6.6 in 1991, adjusted by the World Population). The age-adjusted incidence rate has also been rising since 1975. Age-specific rates have been increasing particularly in the age range 40-79 years. The multiplicative models disclosed an increasing cohort effect for the mortality and incidence rates among women born after 1900. Decreasing mortality and incidence rates after menopause were ascribed by the models to strong cohort effects.

Conclusions: The recently increasing trend was believed to be consistent with changed risk factors among Japanese women. The age effect on female breast cancer incidence rate in Japan was concluded to be similar to that in Western populations.