PAX-2 is a homeogene strongly expressed during development of the genitourinary tract, including the kidney and both wolffian- and müllerian-derived tissues. Expression of PAX-2 by immunohistochemistry has been studied mainly in renal epithelial neoplasms with little attention to the lower male genitourinary tract. We studied PAX-2 expression in epithelium of normal seminal vesicle, normal ejaculatory duct, normal prostatic secretory epithelium, and prostatic adenocarcinoma to define its immunoreactivity pattern throughout the prostate gland and to evaluate its potential diagnostic role in the discrimination of seminal vesicle/ejaculatory duct epithelium from prostatic adenocarcinoma. In addition, given that PAX-2 is highly expressed in tissues of wolffian duct embryologic origin, we also sought to confirm the divergent embryogenesis of the central zone, seminal vesicle, and ejaculatory duct from other regions of the prostate. Prostatectomy specimens from 12 patients were reviewed to identify blocks containing seminal vesicle, ejaculatory duct, periurethral glands, benign prostatic glands, and prostatic acinar adenocarcinoma. A total of 35 blocks from the 12 patients were evaluated. In addition, 2 tissue microarrays representing 15 additional seminal vesicles and 45 prostatic adenocarcinomas, 7 whole sections from prostatic adenocarcinomas of the central zone, and 5 core needle biopsies of seminal vesicle were also evaluated with anti-PAX-2 antibody. In the 12 radical prostatectomy whole sections, nuclear reactivity for PAX-2 was identified in 12 (100%) of 12 of the seminal vesicle epithelium, 9 (90%) of 10 of the ejaculatory duct epithelium, 0 of 12 of the prostatic adenocarcinoma, and 0 of 6 of the high-grade prostatic intraepithelial neoplasia. All 20 total additional seminal vesicles were positive for PAX-2 in the tissue microarray and biopsies; and all 52 additional prostatic adenocarcinomas were negative, including 7 of central zone origin. The staining intensity and percentage of immunoreactive cells in seminal vesicle were both 3+ in all cases. Although the ejaculatory ducts also showed diffuse staining, their staining intensity was less (2+) than that in the seminal vesicles, particularly in the ejaculatory ducts in the periurethral area (1-2+intensity). The smaller glands surrounding the main seminal vesicle duct also showed less intense staining than the luminal cells of the main duct. Of the 19 total cases with evaluable central zone glands, 2 (10.5%) had focal nuclear reactivity in normal, benign prostatic secretory cells. All other benign prostatic secretory epithelia from the peripheral and transition zones were negative for PAX-2. In conclusion, nuclear PAX-2 immunoreactivity is typical in epithelium of the seminal vesicle and ejaculatory duct; but the intensity of staining is less in the ejaculatory duct. No reactivity for PAX-2 was seen in prostatic adenocarcinoma or high-grade prostatic intraepithelial neoplasia. PAX-2 has diagnostic utility as a positive immunohistochemical marker of seminal vesicle and ejaculatory duct epithelium. In addition, these data add further support to the proposed embryogenesis of the prostatic central zone, seminal vesicle, and ejaculatory ducts from the wolffian system.
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