Which factors account for the ethnic inequalities in stage at diagnosis and cervical cancer survival in New Zealand?

Objective: There are substantial ethnic inequalities in stage at diagnosis and cervical cancer survival in New Zealand. We assessed what proportions of these differences were due to screening history (for the analyses of late stage diagnosis), stage at diagnosis (for the analyses of survival), comorbid conditions (for the analyses of survival), and travel time to the nearest General Practitioner and cancer centre. Methods: The study involved 1594 cervical cancer cases registered during 1994-2005. We used G-computation to assess the validity of the estimates obtained by standard logistic regression methods. Results: Māori women had a higher risk of late stage diagnosis compared with 'Other' (mainly European) women (odds ratio (OR) = 2.71; 95% confidence interval 1.98, 3.72); this decreased only slightly (OR 2.39; 1.72, 3.30) after adjustment for screening history, and travel time to the nearest General Practitioner and cancer centre. In contrast, the (non-significantly) elevated risk in Pacific women (1.39; 0.76, 2.54) disappeared almost completely when adjusted for the same factors (1.06; 0.57, 1.96). The hazard ratio of mortality for cervical cancer for Māori women was 2.10 (1.61, 2.73) and decreased to 1.45 (1.10, 1.92) after adjustment for stage at diagnosis, comorbid conditions, and travel time to the nearest General Practitioner and cancer centre; the corresponding estimates for Pacific women were 1.96 (1.23, 3.13) and 1.55 (0.93, 2.57). The G-computation analyses gave similar findings. Conclusions: The excess relative risk of late stage diagnosis in Māori women remains largely unexplained, while more than half of the excess relative risk of mortality in Māori and Pacific women is explained by differences in stage at diagnosis and comorbid conditions.