Stromal nodules in benign prostatic hyperplasia: morphologic and immunohistochemical characteristics

One hundred forty nine stromal nodules (SNs) from transurethral resection of benign prostatic hyperplasia specimens in 39 patients (57-85 years with mean of 70.9) were investigated to characterize the SNs and to outline the etiopathogenesis of solitary fibrous tumors (SFTs) and gastrointestinal stromal tumors (GISTs) of prostate by immunohistochemistry performed on tissue microarray sections.

Antibodies used included smooth muscle actin, desmin, vimentin, and S-100 protein for subtyping, vascular endothelial growth factor, insulin-like growth factor-1, fibroblast growth factor, and TGF-ß as growth factors; CD133, c-KIT, CD34, and CD44 as stem cell markers; and estrogen (ER), progesterone (PR), and androgen receptor (AR) as hormone receptors.

SNs were classified into four subtypes: (1) immature mesenchymal (n = 7, 4.7%); (2) fibroblastic (n = 74, 49.7%); (3) fibromuscular (n = 53, 35.6%); and (4) smooth muscular (n = 15, 10.1%) types. There were linear trends of the expression of all growth factors (VEGF, IGF-1, FGF, TGF-ß), but only CD44 stem cell marker and AR hormone receptor as maturation progressed from immature mesenchymal to smooth muscular type (Ptrend  < 0.05). S-100, c-KIT, and ER were not expressed in any types of SNs. CD34 was positive in 55% of the SNs (82/149).

The data suggest that AR and growth factors are important factors for maturation of SNs, but not influenced by the administration of 5-alpha reductase inhibitor (5ARI). Although the cells comprising the SNs seem to be not associated with the origin of prostatic GISTs, there is a possibility of a tentative link of SFTs arising from SNs of the prostate.