Does comorbidity explain the ethnic inequalities in cervical cancer survival in New Zealand? A retrospective cohort study

Naomi Brewer,Mona Jeffreys,Diana Sarfati,Steven T Fleming,Soo Cheng,Barry Borman,Neil Pearce

doi:10.1186/1471-2407-11-132

Abstract

BackgroundThere are large ethnic differences in cervical cancer survival in New Zealand that are only partly explained by stage at diagnosis. We investigated the association of comorbidity with cervical cancer survival, and whether comorbidity accounted for the previously observed ethnic differences in survival.MethodsThe study involved 1,594 cervical cancer cases registered during 1994-2005. Comorbidity was measured using hospital events data and was classified using the Elixhauser instrument; effects on survival of individual comorbid conditions from the Elixhauser instrument were also assessed. Cox regression was used to estimate adjusted cervical cancer mortality hazard ratios (HRs).ResultsComorbidity during the year before diagnosis was associated with cervical cancer-specific survival: those with an Elixhauser count of ≥3 (compared with a count of zero) had a HR of 2.17 (1.32-3.56). The HR per unit of Elixhauser count was 1.25 (1.11-1.40). However, adjustment for the Elixhauser instrument made no difference to the mortality HRs for Māori and Asian women (compared to 'Other' women), and made only a trivial difference to that for Pacific women. In contrast, concurrent adjustment for 12 individual comorbid conditions from the Elixhauser instrument reduced the Māori HR from 1.56 (1.19-2.05) to 1.44 (1.09-1.89), i.e. a reduction in the excess risk of 21%; and reduced the Pacific HR from 1.95 (1.21-3.13) to 1.62 (0.98-2.68), i.e. a reduction in the excess risk of 35%.ConclusionsComorbidity is associated with cervical cancer-specific survival in New Zealand, but accounts for only a moderate proportion of the ethnic differences in survival.

Highlights

There are large ethnic differences in cervical cancer survival in New Zealand that are only partly explained by stage at diagnosis
In New Zealand, comorbidity has been found to contribute to ethnic-specific survival disparities for colon cancer [12], the management of stages I and II non-small-cell lung cancer [13], and adverse event status, inpatient death and increased length of stay in selected Auckland hospitals [14]
We found very similar results with the two comorbidity measures, and we have only reported the findings for the Elixhauser instrument; effects on survival of individual comorbid conditions from the Elixhauser instrument were assessed

Summary

Introduction

There are large ethnic differences in cervical cancer survival in New Zealand that are only partly explained by stage at diagnosis. In 2005, cervical cancer was the ninth most common site of cancer registration for New Zealand females [1], and the incidence and mortality rates were moderately high compared with the rest of the developed world [2]. We have previously reported demographic differences in cervical cancer survival in New Zealand [3]. In New Zealand, comorbidity has been found to contribute to ethnic-specific survival disparities for colon cancer [12], the management of stages I and II non-small-cell lung cancer [13], and adverse event status, inpatient death and increased length of stay in selected Auckland hospitals [14]. Comorbidity has been found to adversely affect survival in patients with a range of conditions, including cervical cancer [15,16,17,18,19,20,21]

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Results

Conclusion