Purpose: The insulin-like growth factor system has recently been shown to have important mitogenic effects in the prostate. The system consists of 2 ligands: insulin-like growth factor types 1 and 2, which are potent mitogens for prostate cell growth, and 6 insulin-like growth factor binding proteins that modify the activity of these growth factors. Recently, changes in serum levels of insulin-like growth factor binding proteins 2 and 3 have been identified in prostate cancer patients but in vivo studies of these changes have not been previously reported.
Materials and methods: We performed immunohistochemical staining for insulin-like growth factor binding proteins 2 and 3 in areas of benign disease, prostatic intraepithelial neoplasia, and cancer from specimens obtained from 24 patients who underwent prostatectomy to determine changes in the quantity of these proteins with progression from the benign through the premalignant and into the malignant states. Quantification of the differences noted in the amount of insulin-like growth factor binding proteins 2 and 3 found in each of the 3 tissue types was then correlated with serum and tissue prostate specific antigen levels, pathological stage and grade of the tumors.
Results: Our data indicate that as human prostate tissue progresses from the benign to the malignant state, insulin-like growth factor binding protein 2 immunoreactivity in the prostatic luminal epithelial cells increases and that of insulin-like growth factor binding protein 3 decreases. Quantification of the differences noted in binding proteins 2 and 3 among all 3 tissue types was statistically significant. However, no correlation was noted between the stage or grade of prostate carcinoma and insulin-like growth factor binding protein 2 or 3 immuno-staining intensity. Additionally, no significant correlation was found between serum or tissue levels of prostate specific antigen and insulin-like growth factor binding protein 2 or 3 immunoreactivity.
Conclusions: Our data suggest that significant changes in the insulin-like growth factor system occur with malignant transformation in the prostate. It is hoped that this system may eventually result in a better serum or tissue (from prostate biopsy) marker of malignant transformation, and/or represent a target for early therapeutic intervention to alter the growth and development of prostate cancer.