Ethnic disparity in colonic cancer outcomes in New Zealand – biology or an access issue?

BACKGROUND: There is an ethnic variation in outcomes for colonic cancer in New Zealand. Whether this disparity is caused by cancer biology or inequitable provision of treatment services after diagnosis has not been elucidated. METHOD: National cancer registry data from 1996 to 2003 were obtained. Incidence and mortality rates for the four major ethnic groups were age-adjusted to the new WHO world population. The impact of age, sex, AJCC stage and site of cancer at diagnosis was compared between ethnic groups using a Cox regression analysis. RESULTS: A total of 11 987 colonic cancer registrations were identified. The overall raw 5-year mortality was 53.7%. The age-adjusted incidence in Europeans was more than double that of the Maori, Asian and Pacific populations at 33.0 per 100,000 population/year. Europeans presented at a greater age, with more right sided cancers, and at an earlier stage of disease. The opposite was true for the Maori population. Pacific Islanders and Asians presented at a younger age, but with a similar site, stage and sex distribution to the rest of the population. There were no significant differences in 5 year mortality after diagnosis when age, sex, stage, and site at presentation were controlled for by cox regression analysis. CONCLUSION: These results suggest that age, sex, stage and site at presentation may be more important than inequality in treatment provision after diagnosis in explaining differences in outcomes between the ethnicities. Efforts need to be focused on identifying reasons for the increased risk of colonic neoplasia in Europeans and the later stage disease presentation in the Maori population.