Systematic review of population‐based bladder cancer registries: How criteria heterogeneity affects the comparison of incidences

BACKGROUND: The population‐based registry of bladder cancer (BC) raises specific problems intrinsic to the tumor, as the inclusion of noninfiltrating, potentially malignant and multiple tumors. We performed a systematic review (PRISMA guidelines) of population‐based BC registries to obtain information on their geographic areas involved, last dates of real incidence of BC, and rules coding used in BC for uncertain behavior, in situ and multiple tumors. METHODS: Using MEDLINE and Google Scholar, we identified scientific publications of in the last 10 years in English or Spanish, whether they were related to a national or international cancer registry, provided information on registry rules, and provided data on the incidence of BC. RESULTS: After the first screening, a total of 194 references were obtained. After a second analysis, three registries were selected: International Agency for Research on Cancer (IARC) is a world registry providing real incidence of BC in the period 2008–2012. Surveillance, Epidemiology, and End Results (SEER) Program registered incidence until 2017 in more than 90% of the US population. Spanish Network of Cancer Registries (REDECAN) unifies 14 Spanish registries (27.4% of the population) with real incidence data from 2010 to 2015. The coding and inclusion rules have been modified, but currently, most registries include BC in situ and uncertain behavior tumors. Whenever a new case occurs 36 months after a previous diagnosis, SEER registers those as multiple incident cancers in the same location, while IARC and REDECAN only allow one cancer per location during the lifespan of the patient. CONCLUSIONS: Comparison of the incidence of BC among different population‐based cancer registries is prone to bias due to the methodological differences regarding the inclusion of carcinomas in situ, indeterminate, and multiple tumors. A good cancer registry could provide better surveillance strategies for BC patients.