Why have ovarian cancer mortality rates declined? Part I. Incidence.

The age-adjusted mortality rate from ovarian cancer in the United States has declined over the past several decades. The decline in mortality might be the consequence of a reduced number of cases (incidence) or a reduction in the proportion of patients who die from their cancer (case-fatality). In part I of this three-part series, we examine rates of ovarian cancer incidence and mortality from the Surveillance Epidemiology and End Results (SEER) registry database and we explore to what extent the observed decline in mortality can be explained by a downward shift in the stage distribution of ovarian cancer (i.e. due to early detection) or by fewer cases of ovarian cancer (i.e. due to a change in risk factors). The proportion of localized ovarian cancers did not increase, suggesting that a stage-shift did not contribute to the decline in mortality. The observed decline in mortality paralleled a decline in incidence. The trends in ovarian cancer incidence coincided with temporal changes in the exposure of women from different birth cohorts to various reproductive risk factors, in particular, to changes in the use of the oral contraceptive pill and to declining parity. Based on recent changes in risk factor propensity, we predict that the trend of the declining age-adjusted incidence rate of ovarian cancer in the United States will reverse and rates will increase in coming years.