IGFI genotype, mean plasma level and breast cancer risk in the Hawaii/Los Angeles multiethnic cohort

The insulin-like growth factor I gene (IGFI) is a strong candidate gene for a breast cancer susceptibility model. We investigated a dinucleotide repeat 969 bp upstream from the transcription start site of the IGFI gene for possible associations with plasma IGFI levels and breast cancer risk in a multiethnic group of postmenopausal women. Furthermore, we investigated the relation between race/ethnicity, mean plasma IGFI levels and breast cancer rates in the Hawaii/Los Angeles Multiethnic Cohort. The mean age-adjusted IGFI level among Latino-American women, 116 ng ml(-1), was statistically significantly lower than the mean age-adjusted IGFI levels for each of the three other racial/ethnic groups, African-American, Japanese-American and Non-Latino White women (146, 144 and 145 ng ml(-1), respectively) (P<0.0001). Latino-American women have the lowest breast cancer rates of any racial/ethnic group in the cohort. These results support the investigation of an expansion of the hypothesis for an important role of IGFI in breast cancer tumorigenesis to different racial/ethnic groups and to postmenopausal women. It is unlikely that any involvement of IGFI in breast cancer aetiology is mediated by the IGFI dinucleotide repeat polymorphism, which was not significantly associated with circulating IGFI levels nor breast cancer risk in this study. Research into relevant determinants of IGFI levels in the blood must continue. (C) 2003 Cancer Research UK.