TRENDS IN COLORECTAL-CANCER INCIDENCE AND HISTOLOGIC-FINDINGS IN MAORI AND POLYNESIAN RESIDENTS OF NEW-ZEALAND

Background. The aim of this study was to combine an epidemiologic surv ey of colorectal cancer among Maori, Polynesian, and white inhabitants of New Zealand with a detailed analysis of tumor subsite and histopat hology. Methods. Data were obtained from the New Zealand National Canc er Registry and included all registrants from 1970 to 1984. Sections o f histologic specimens of colorectal cancer of Maori and non-Maori wer e retrieved from three Auckland hospitals. Results. The annual age-adj usted incidence rates of large intestinal cancer among male and female Maoris and male and female Polynesians were 40%, 40%, 39%, and 29%, r espectively, of the total population incidence. Time-trend analysis sh owed the incidence of large intestinal cancer to be increasing among a ll 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. Carc inomas were diagnosed at a more advanced stage in Maoris. Conclusion. Given the similar environmental characteristics of the three racial gr oups, the findings indicate the presence of powerful protective factor s in Maoris and Polynesians. These could be constitutional or mediated by unrecognized dietary constituents. Cancer