Comparing cancer profiles and survival of aboriginal and non-aboriginal patients in South Australia: where are the opportunities for improving Aboriginal health?

Abstract

Data from the South Australian Cancer Registry (SACR) for 1977-2003 were used to calculate expected and actual distributions of cancer sites in Aboriginal versus non-Aboriginal populations. Expected distributions were calculated using indirect standardisation and compared with actual distributions using a global Chi-square test. Individual contributions to the Chi-square statistic (from each cancer site) were examined using a z-test and Bonferroni corrected p-value. The expected figure for each cancer site corresponds to the number of cancers we would have expected in Aboriginal patients if they had the same cancer distribution of site by age as the non-Aboriginal population. Expected 5- and 10-year survivals were also calculated and compared to expected survivals drawn from Statewide survivals adjusted for age at diagnosis. There was an overall significant difference in expected and actual cancer site distributions for South Australian Aboriginal male (c2 (17df) = 202.94) and female (c2 (20df) = 311.93) patients, and all patients collectively (c2 (22df) = 485.43). Aboriginal patients had poorer expected 5- and 10-year survival compared with South Australian non-Aboriginal patients, and even poorer actual 5- and 10-year survival than expected. The differences between the expected and actual cancer site distributions reflect the disparities in risk factor prevalence for largely preventable cancers and the survival results reflect the multitude of obstacles confronting Aboriginal patients with cancer compared with non-Aboriginal cancer patients. This study provides areas of focus for interventions to reduce cancer levels in the Aboriginal population and to improve survival of Aboriginal people diagnosed with cancer.