Racial differences in insulin-like growth factor binding protein-3 in men at increased risk of prostate cancer

Objectives. To determine the overall plasma levels of insulin-like growth f actor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-5) in a group of men at higher risk of prostate cancer development and to inve stigate the relationships between demographics and these levels, particular ly with regard to race. Methods. An enzyme-linked immunosorbant assay was used to quantitate plasma levels of IGF-1 and IGFBP-3. The study group consisted of 105 men (65 Afri can American [AA], 42 white), aged 35 to 69 years, with no personal history of prostate cancer, but having at least one first-degree relative diagnose d with the disease, unless they were AA. Differences in plasma levels and c ategorical covariates were assessed using the nonparametric Wilcoxon test. Associations between plasma levels and the continuous variables were quanti fied using the nonparametric Spearman correlation coefficient. Results. The mean plasma level of IGF-1 was not significantly different bet ween AA (162.3 ng/mL) and white (172.1 ng/mL) men (P = 0.415). However, the mean plasma level of IGFBP-3 was lower in AA (2789 ng/mL) than in white (3 216 ng/mL) men, and this decrease was highly significant (P = 0.0045). No c orrelation between IGFBP-3 plasma level and age was detected in the group a s a whole, but an inverse relationship between IGF-1 plasma level and age w as evident (P = 0.0079). Conclusions, Our results demonstrate that IGFBP-3 plasma levels are lower i n AA men than in white men. Since IGFBP-3 can control IGF-1 bioavailability , the lowered IGFBP-3 could explain in part the increased risk of prostate cancer in AA men. UROLOGY 54: 178-182, 1999. (C) 1999, Elsevier Science Inc .