Decreased immunoexpression of prostate inhibin peptide in prostatic carcinoma: a study with monoclonal antibody

Prostate inhibin peptide (PIP) is a follicle-stimulating hormone (FSH) regulating peptide produced by the prostate. The mechanism of its endocrine role in regulating prostate growth is believed to be androgen-independent but FSH-dependent. Previous studies using polyclonal antibody proposed PIP as a prostatic-specific marker in cancer diagnosis. However, the recently available monoclonal antibody has not yet been evaluated. Paraffin sections of 72 prostatectomy specimens for prostate cancer with or without hormonal blockage therapy and 10 nonneoplastic prostate tissues from autopsy were stained by using PIP monoclonal antibody (clone: 4A6A6) with the avidin-biotin complex method. PIP reactivity was semiquantitatively estimated in prostatic carcinoma (PCA), prostatic intraepithelial neoplasia (PIN), benign prostatic hyperplasia (BPH) and normal tissue in each case when ever present. Statistical analyses were performed accordingly. PIP expression is predominantly cytoplasmic. Urothelium, seminal vesicles, inflamed prostatic glands, basal cells, and squamous metaplasia were negative for PIP. Average percentage of cells expressing PIP was significantly decreased in PIN (40%) and PCA (14%) when compared with BPH (81%) and normal tissue (68%). There was no correlation of tumor PIP level with patient's age, tumor size, Gleason score, tumor stage, or the usage of preoperative hormonal blockage therapy. PIP monoclonal antibody should be used with caution as a prostate-specific marker in surgical pathology. The mechanism for this alteration and the effect of PIP on prostatic tumor growth, particularly in patients under a variety of hormonal therapies, needs further study.