Trends in the Incidence of Female Breast and Cervical Cancers in Miyagi Prefecture, Japan, 1959–1987

Trends in the incidence of female breast and cervical cancers were examined, using the cancer registry data in Miyagi Prefecture, Japan, during 1959–1987. The age‐standardized incidence rate of breast cancer has been increasing, while that of cervical cancer has been decreasing. Age‐period‐cohort models were applied to clarify the trends in incidence. For breast cancer incidence, the age‐period model adequately represented the data, and demonstrated that the risk of developing breast cancer has been increasing in recent time periods. The effect of cohort on breast cancer incidence was insignificant and the full model containing age, period and cohort showed irregularities in the cohort effect. For cervical cancer incidence, the effect of period was significant, while the effect of cohort was marginal. The full model containing age, period and cohort showed that cervical cancer risk has been decreasing in recent time periods and younger birth cohorts. Using published reports, we investigated the trends in the prevalence of various risk factors and compared them with the trends in the incidence at both sites. It is suggested that the effects of period and cohort might be related to the changes in the prevalence of these risk factors as well as to improvements of the diagnostic procedures.