Trends in the mortality (1950-1997) and incidence (1975-1993) of malignant ovarian neoplasm among Japanese women: Analyses by age, time, and birth cohort

Objective. The purpose of this study was to explore epidemiological features of malignant ovarian neoplasm in Japan. Methods. The number of deaths from malignant ovarian neoplasm was obtained from the national vital statistics. Estimated incidence rates, based on several cancer registries, were also used for analyses. We divided the subjects into two age groups (0-29 and 30+ years) and examined secular trends in mortality (1950-1997) and incidence (1975-1993) by age, time, and birth cohort. Results. The age-adjusted mortality rate has increased approximately 4-fold (from 0.9 to 3.6 per 100,000 women) from 1950 to 1997. Age-specific mortality rates showed a rising pattern in the elderly, whereas mortality in the younger people tended to increase in the 1950s and 1960s, but then decreased in the 1970s and afterward. In analyses using a mathematical model, the time effect in the population aged 0-29 years increased with advancing period up to 1970, and then decreased. The cohort effects had positive values, which indicate higher than additive influence from age/time effect, for birth cohorts from 1900 to 1935. The age-adjusted incidence rate increased approximately 1.5-fold (from 3.6 to 5.7) from 1975 to 1993. The rate increased in the early 1980s, but has remained stable since the late 1980s. Age-specific incidence rates in older age groups increased steadily up to 1985, and have remained stable since, while the rates in younger women have remained almost unchanged. Conclusion. The major effects on malignant ovarian neoplasm in Japan are supposed to be due to declining parity and therapeutic improvements.