Estimated and observed cancer incidence in Italy: a validation study

AIMS AND BACKGROUND: The study aimed to validate model-based incidence estimates by means of observed incidence rates provided by Italian cancer registries, for five major cancer sites (stomach, colon and rectum, lung, breast and prostate cancers) and for all cancers together. METHODS: Recent incidence rates observed by Italian population-based cancer registries were extracted from the data base of the Italian Association of Cancer Registries. Regional estimates of incidence rates for the same cancers were obtained by the MIAMOD method. Observed and estimated crude incidence rates and incidence trends were compared for the period of diagnosis 1985-2000. Eight Italian cancer registries and seven regions were selected for the analysis since they had incidence data available during the entire selected period. RESULTS AND CONCLUSIONS: An excellent agreement between estimated and observed crude incidence rates was found for all single cancer sites, regarding absolute incidence levels and time trends. A partial exception was breast, where empirical data showed a sudden increase in the last three years of observation, perhaps due to organized screenings in some Italian regions, and not captured by statistical models. Substantial underestimation of model-based incidence rates was found for all cancers combined, where the difference tended to increase with calendar year, up to a maximum of 20% in recent years. The greatest part of the discrepancy can be attributed to multiple cancers, which were included in cancer registries statistics but were not accounted for in MIAMOD estimates.