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

Lettie Pule, Elizabeth Buckley, Theophile Niyonsenga, David Banham, David Roder

Research output: Contribution to journalArticle

Abstract

BACKGROUND: Comorbidity 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.

METHODS: A 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.

RESULTS: The 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.

CONCLUSIONS: Our 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.

Original languageEnglish
Pages (from-to)776
JournalBMC Health Services Research
Volume18
Issue number1
DOIs
Publication statusPublished - 16 Oct 2018

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Comorbidity
Neoplasms
Survival
Hypertension
Weights and Measures
Cancer Care Facilities
Mortality
Diabetes Complications
Proportional Hazards Models
Social Class
Chronic Obstructive Pulmonary Disease
Registries
Inpatients
Cohort Studies
Retrospective Studies
Parturition

Cite this

Pule, Lettie ; Buckley, Elizabeth ; Niyonsenga, Theophile ; Banham, David ; Roder, David. / Developing a comorbidity index for comparing cancer outcomes in Aboriginal and non-Aboriginal Australians. In: BMC Health Services Research. 2018 ; Vol. 18, No. 1. pp. 776.
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Developing a comorbidity index for comparing cancer outcomes in Aboriginal and non-Aboriginal Australians. / Pule, Lettie; Buckley, Elizabeth; Niyonsenga, Theophile; Banham, David; Roder, David.

In: BMC Health Services Research, Vol. 18, No. 1, 16.10.2018, p. 776.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Developing a comorbidity index for comparing cancer outcomes in Aboriginal and non-Aboriginal Australians

AU - Pule, Lettie

AU - Buckley, Elizabeth

AU - Niyonsenga, Theophile

AU - Banham, David

AU - Roder, David

PY - 2018/10/16

Y1 - 2018/10/16

N2 - BACKGROUND: Comorbidity 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.METHODS: A 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.RESULTS: The 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.CONCLUSIONS: Our 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.

AB - BACKGROUND: Comorbidity 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.METHODS: A 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.RESULTS: The 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.CONCLUSIONS: Our 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.

KW - Adult

KW - Aged

KW - Australia/epidemiology

KW - Comorbidity

KW - Diabetes Mellitus/ethnology

KW - Female

KW - Humans

KW - Hypertension/ethnology

KW - Male

KW - Middle Aged

KW - Neoplasms/ethnology

KW - Oceanic Ancestry Group

KW - Prevalence

KW - Proportional Hazards Models

KW - Retrospective Studies

KW - Risk Assessment

KW - South Australia/epidemiology

U2 - 10.1186/s12913-018-3603-y

DO - 10.1186/s12913-018-3603-y

M3 - Article

VL - 18

SP - 776

JO - BMC Health Services Research

JF - BMC Health Services Research

SN - 1472-6963

IS - 1

ER -