Estimating cancer incidence in Indigenous Australians.

OBJECTIVE: To assess data quality of cancer registrations for Indigenous Australians and produce reliable national Indigenous cancer incidence statistics.
METHODS: Completeness of Indigenous identification was assessed for the eight Australian cancer registries using an innovative indirect assessment method based on registry-specific registration rates for smoking-related cancers. National age-standardised incidence rates and rate ratios (Indigenous:non-Indigenous) were calculated for all cancers combined and 26 individual cancer sites. Multivariate regression analysis was used to investigate trends in Indigenous cancer incidence by time or remoteness of residence, and whether the incidence rate ratio (Indigenous:non-Indigenous) was different in younger than older age-groups.
RESULTS: Four registries covering 84% of the Indigenous population had sufficiently complete Indigenous identification to be included in analysis. Compared to other Australians, Indigenous Australians had much higher incidence of lung and other smoking-related cancers, cervix, uterus and liver cancer, but much lower incidence of breast, prostate, testis, colorectal and brain cancer, melanoma of skin, lymphoma and leukaemia. Incidence was higher in remote areas for some cancers (including several smoking-related cancers) but lower for others. The incidence rate ratios (IRRs) for smoking-related cancers were higher in younger than older people.
CONCLUSIONS: Indigenous Australians have a different pattern of incidence of specific cancers than other Australians and large geographical variations for several cancers. IMPLICATIONS: All cancer registries need to further improve Indigenous identification, but national Indigenous cancer incidence statistics can, and should, be regularly reported. Tobacco control is a critical cancer-control issue for Indigenous Australians.