A mathematical estimation of true cancer incidence using data from population-based cancer registries

Background: Accurate cancer incidence data are needed to plan, monitor and evaluate national cancer control programs. In Japan, however, such information is not available owing to incomplete cancer registries. In order to attain incidence estimation adjusted to account for this incomplete information, we have developed a new method. Methods: We developed a nonlinear regression model between observed incidence/mortality ratios and proportions of death certificate notification to observed incidence in various cancer registries. This model enables us to obtain the 'true incidence/mortality ratio', which, in the regression curve, is at zero point for the proportion of death certificate notifications. This is an ideal registration state without any missing cases. By multiplying it by the number of cancer mortalities from the National Vital Statistics, corrected cancer incidence can be estimated. Results: Applying this method for the estimation of the Japanese cancer incidence in 1997, we obtained the 'true incidence/mortality ratios' of 2.074 for men and 2.587 for women. Cancer incidences in Japan for 1997 were thus estimated to be 346 000 for men and 280 000 for women. Conclusions: A new method is proposed to estimate the national cancer incidence after adjusting for completeness of cancer registries. This method enables us to more accurately estimate the cancer incidence in a country where several cancer registries exist with various degrees of completeness of registration.