Developing a comorbidity index for comparing cancer outcomes in Aboriginal and non-Aboriginal Australians

Abstract

BackgroundComorbidity is known to increase risk of death in cancer patients, both Aboriginal and non-Aboriginal. The means of measuring comorbidity to assess risk of death has not been studied in any depth in Aboriginal patients in Australia. In this study, conventional and customized comorbidity indices were used to investigate effects of comorbidity on cancer survival by Aboriginal status and to determine whether comorbidity explains survival disparities.MethodsA retrospective cohort study was undertaken using linked population-based South Australian Cancer Registry and hospital inpatient data for 777 Aboriginal people diagnosed with primary cancer between 1990 and 2010 and 777 randomly selected non-Aboriginal controls matched by sex, birth year, diagnosis year and tumour type. A customised comorbidity index was developed by examining associations of comorbid conditions with 1-year all-cause mortality within the Aboriginal and non-Aboriginal patient groups separately using Cox proportional hazard model, adjusting for age, stage, sex and primary site. The adjusted hazard ratios for comorbid conditions were used as weights for these conditions in index development. The comorbidity index score for combined analyses was the sum of the weights across the comorbid conditions for each case from the two groups.ResultsThe two most prevalent comorbidities in the Aboriginal cohort were “uncomplicated” hypertension (13.5%) and diabetes without complications (10.8%), yet in non-Aboriginal people, the comorbidities were “uncomplicated” hypertension (7.1%) and chronic obstructive pulmonary disease (4.4%). Higher comorbidity scores were associated with higher all-cause and cancer-specific mortality. The new index showed minor improvements in predictive ability and model fit when compared with three common generic comparison indices. After accounting for the competing risk of other deaths, stage at diagnosis, socioeconomic status, area remoteness and comorbidity, the increased risk of cancer death in Aboriginal people remained.ConclusionsOur new customised index performed at least as well, although not markedly better than the generic indices. We conclude that in broad terms, the generic indices are reasonably effective for adjusting for comorbidity when comparing survival outcomes by Aboriginal status. Irrespective of the index used, comorbidity has a negative impact on cancer-specific survival, but this does not fully explain the lower survival in Aboriginal patients.

The burden of chronic diseases among Australian cancer patients: Evidence from a longitudinal exploration, 2007-2017

“…For instance, the mortality rate is substantially higher among cancer patients with comorbidities (47%) compared with cancer patients without comorbidities (34%) [19]. Given the clinical significance of comorbidity and its high prevalence in cancer survivors, it is essential to have a measure for quantifying likely effects on cancer outcomes [20]. Understanding more about comorbidities among cancer patients can generate possible evidence as well as provide direction for prevention, management, and treatment of chronic diseases.…”

Factors associated with cancer survival disparities among Aboriginal and Torres Strait Islander peoples compared with other Australians: A systematic review

“…There was a consistent pattern of poorer survival among Aboriginal and Torres Strait Islander peoples for seven ( 3 , 6 , 30 , 31 , 34 – 36 ) state-based studies that reported unadjusted estimates ( Table 3 ; Supplementary materials Table S1.5 ). Of the six studies that also reported estimates adjusted for various combinations of potential explanatory factors (other than age or sex), five found that the disparity reduced in magnitude after adjustment for remoteness, SES, and either cancer stage at diagnosis ( 34 – 36 ), or broad cancer group ( 6 , 30 ) although it was still elevated and statistically significant. However, the remaining study, over an earlier time-period with less complete cultural identification, found that the adjusted differential was only elevated in magnitude and statistically significant up to one year after cancer diagnosis ( 31 ).…”

“…The majority (n=27) of studies reported cause-specific survival while three reported relative survival ( 4 , 5 , 39 ). Most studies focused on short to medium-term survival while seven did not specifically provide this information about length of follow-up ( 34 – 36 , 39 , 40 , 44 , 47 ). A variety of statistical models were used to quantify the survival differential by Aboriginal and Torres Strait Islander status and suggest associative factors ( Figure 3 ).…”

The ‘ABC’ of respiratory disorders among adult Indigenous people: asthma, bronchiectasis and COPD among Aboriginal Australians – a systematic review

“…Of the 30 studies which reported on COPD (including the three studies which combined asthma and COPD),15 37 38 a single study reported community cross-sectional data,39 while the remainder reported on referred populations (table 3). Fourteen studies reported on patients presenting to hospital,29 33 37 38 40–44 53 54 57–59 12 on patients referred to a respiratory health service,7 14 15 30 45 46 48–52 60 and one each on patients using DOT,47 patients newly diagnosed with lung cancer,34 and patients diagnosed with obstructive sleep apnoea 61. The combined mean age of participants was 52.5±15.3 years,30 34 39 42 46 57 which varied by geography, with participants from the largest NT, CA study with a mean of 45.2±15.8 years,42 Kimberley region participants 51.8±9.3 years,39 from the largest NT, TEHS region study 51.3±12.3 years,46 SA participants 57.7±15.6 years34 and WA participants 54±15.4 years 57.…”