Objectives: To determine the overall plasma levels of insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) in a group of men at higher risk of prostate cancer development and to investigate the relationships between demographics and these levels, particularly 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 (63 African American [AA], 42 white), aged 35 to 69 years, with no personal history of prostate cancer, but having at least one first-degree relative diagnosed with the disease, unless they were AA. Differences in plasma levels and categorical covariates were assessed using the nonparametric Wilcoxon test. Associations between plasma levels and the continuous variables were quantified using the nonparametric Spearman correlation coefficient.
Results: The mean plasma level of IGF-1 was not significantly different between 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 (3216 ng/mL) men, and this decrease was highly significant (P = 0.0045). No correlation between IGFBP-3 plasma level and age was detected in the group as a whole, but an inverse relationship between IGF-1 plasma level and age was evident (P = 0.0079).
Conclusions: Our results demonstrate that IGFBP-3 plasma levels are lower in 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.