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 exa mined, using the cancer registry data in Miyagi Prefecture, Japan, dur ing 1959-1987. The age-standardized incidence rate of breast cancer ha s been increasing, while that of cervical cancer has been decreasing. Age-period-cohort models were applied to clarify the trends in inciden ce. For breast cancer incidence, the age-period model adequately repre sented the data, and demonstrated that the risk of developing breast c ancer has been increasing in recent time periods. The effect of cohort on breast cancer incidence was insignificant and the full model conta ining age, period and cohort showed irregularities in the cohort effec t, For cervical cancer incidence, the effect of period was significant , while the effect of cohort was marginal. The full model containing a ge, period and cohort showed that cervical cancer risk has been decrea sing 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 si tes. It is suggested that the effects of period and cohort might be re lated to the changes in the prevalence of these risk factors as well a s to improvements of the diagnostic procedures.