Background: The aim of this study was to combine an epidemiologic survey of colorectal cancer among Maori, Polynesian, and white inhabitants of New Zealand with a detailed analysis of tumor subsite and histopathology.
Methods: Data were obtained from the New Zealand National Cancer Registry and included all registrants from 1970 to 1984. Sections of histologic specimens of colorectal cancer of Maori and non-Maori were retrieved from three Auckland hospitals.
Results: The annual age-adjusted incidence rates of large intestinal cancer among male and female Maoris and male and female Polynesians were 40%, 40%, 39%, and 29%, respectively, of the total population incidence. Time-trend analysis showed the incidence of large intestinal cancer to be increasing among all racial groups. The relative proportion of rectal cancers was higher in male and female Maoris and female Polynesians than in the general population, whereas male Polynesians had a relatively high proportion of right colonic cancers. High-grade carcinoma and mucinous carcinoma occurred more frequently in young individuals regardless of race. Carcinomas were diagnosed at a more advanced stage in Maoris.
Conclusion: Given the similar environmental characteristics of the three racial groups, the findings indicate the presence of powerful protective factors in Maoris and Polynesians. These could be constitutional or mediated by unrecognized dietary constituents.