Cervical cancer in Canada: changing patterns in incidence and mortality.

Data on incidence of cervical cancer by histologic subtype and mortality for the Canadian provinces of Ontario, Saskatchewan, and British Columbia were used to examine time trends by age, calender period, and birth cohort. Age-adjusted incidence rate of squamous cell carcinoma of the cervix decreased from 11.1 per 100,000 women in 1970-72 to 5.3 in 1994-96, while the rate for cervical adenocarcinoma increased from 1.1 per 100,000 women to 1.5 over the same period. Age-adjusted mortality rate declined from 7.9 per 100,000 women in 1953-55 to 1.9 in 1995-97. The patterns in age-specific mortality rates in 1953-72 were different from those in 1973-97; younger women experienced larger reductions in mortality during the earlier period while older women benefited to a greater extent during the latter period. Age-period-cohort modeling showed that cohort effects were responsible for the decreasing trends in incidence of squamous cell carcinoma of the cervix and increasing trends in adenocarcinoma, and both period and cohort effects account for the observed trends in mortality. The results suggest that Pap smear screening has played a significant role in the reduction in squamous cell cervical carcinoma. The causes for the increase in cervical adenocarcinoma are unclear.