Quantitative immunohistochemical analysis of insulin-like growth factor binding protein-3 in human prostatic...

We sought to characterize and quantitate the expression of IGFBP-3 in adenocarcinoma of the prostate and to test whether it correlated with tumor differentiation determined by Gleason grade. We also investigated the potential of using IGFBP-3 as a prognostic indicator of clinically localized prostate cancer.

Initially we evaluated the expression of IGFBP-3 in six normal and twenty neoplastic prostates using standard immunohistochemical techniques (study 1). We then obtained radical prostatectomy specimens from twenty-four patients with a preoperative diagnosis of clinically localized prostate adenocarcinoma and five year follow up information, and nine normal prostates from organ donors or from patients undergoing cystoprostatectomy (study 2). All specimens were immunostained with a polyclonal anti-human IGFBP-3 antibody. A single pathologist reviewed all sections and assigned a Gleason grade to each cancer focus. Using computer-assisted video image analysis, we quantified the intensity of IGFBP-3 immunostaining of each cancer focus and of normal controls.

Normal prostatic epithelium showed intense cytoplasmic IGFBP-3 staining. The stromal compartment showed less intense staining, although there were occasional areas with strong immunoreactivity. The cellular distribution of IGFBP-3 staining in prostatic adenocarcinoma was comparable to normal tissue; however, the intensity of detectable staining in neoplastic epithelial cells was significantly decreased. Two foci of prostatic intraepithelial neoplasia (PIN) demonstrated IGFBP-3 immunoreactivity decreased in comparison to normal epithelium, but greater than prostatic adenocarcinoma. Histologically normal epithelium surrounding cancer foci also showed decreased immunostaining for IGFBP-3 compared with normal prostate. The marked decrease in immunostaining intensity of IGFBP-3 in prostate adenocarcinoma was not associated with Gleason grade or with clinical outcome.

Malignant transformation of prostatic epithelium was associated with a significant decrease in the amount of immunoreactive IGFBP-3 (p <0.0001); however, this parameter did not correlate with Gleason grade of the tumor or with patient outcome. The decrease in immunostaining intensity of IGFBP-3 in all Gleason grades and in PIN suggests that lower expression of IGFBP-3 is an early event in prostatic carcinogenesis. The finding that decreased IGFBP-3 immunostaining did not correlate with clinical outcome suggests that this parameter is not a therapy-guiding prognostic indicator for clinically localized prostate cancer.