Mini Oral Australian Epidemiology Association ASM 2018

Developing a comorbidity index for comparing survival from cancer in Aboriginal and non-Aboriginal Australians. (#73)

Lettie Pule 1 , David Roder 1 , David Banham 2 , Theophile Niyonsenga 1 3 , Elizabeth Buckley 1
  1. Centre for Population Health Research, University of South Australia, Adelaide, South Australia, Australia
  2. Wardliparingga Aboriginal Research Unit, South Australian Health and Medical Research , Adelaide , South Australia, Australia
  3. Centre for Research and Action in Public Health, University of Canberra , Canberra, ACT , Australia

Background: Comorbidity is known to increase risk of mortality in cancer patients, both Aboriginal and non-Aboriginal, and particularly at an older age. The best means of measuring comorbidity when comparing survival by Aboriginal status have received limited attention.

Aim: To develop a comorbidity index to test whether comorbidity explains survival differences by Aboriginal status.

Methods: A retrospective cohort study using linked population-based South Australian Cancer Registry and hospital inpatient data for 777 Aboriginal people diagnosed with primary cancer during 1990 – 2010 and 777 randomly selected non-Aboriginal controls matched by sex, birth year, diagnosis year and tumour type. The index was developed by examining statistical associations of comorbid conditions with 1-year all-cause mortality separately for Aboriginal and non-Aboriginal cancer cases,repectively, using Cox proportional hazard model, adjusting for age, stage, sex and primary site. The adjusted hazard ratios were used as weights for these conditions in index development. The comorbidity index score was the sum of the weights for each person across the two groups. Performance of the new index was compared to commonly used indices. 

Results: The new index performed as well as, or marginally better than, other generic indices. Irrespective of the index, comorbidity did not explain the increased risk of mortality in Aboriginal people.

Conclusions: Generic comorbidity indices may be sufficient for comparing comorbidity effects by Aboriginal status. This study showed lower survival for Aboriginal than other patients after adjusting for stage and comorbidity.   

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  2. Sarfati D: Review of methods used to measure comorbidity in cancer populations: No gold standard exists. Journal of Clinical Epidemiology 2012, 65(9):924-933.
  3. Charlson ME, Pompei, P.,Ales, K. L.,Mackenzie, C. R.: A New Method of Classifying Prognostic Co-Morbidity in Longitudinal-Studies - Development and Validation. J Chron Dis 1987, 40(5):373-383.