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Pseudoangiomatous stromal hyperplasia of the prostate: report of an unprecedented entity in prostate pathology.

Pseudoangiomatous stromal hyperplasia is a benign entity of the breast. It is histologically characterized by open, slit-like spaces lined by spindle cells of myofibroblast/fibroblast differentiation in a dense collagenous stroma. Although pseudoangiomatous stromal hyperplasia has been reported in ectopic breast tissue in anogenital mammary-like glands, it has not been previously reported in non-breast tissues. This includes prostatic tissue, which shares similar histology and pathology with the breast. Herein, we report the first case of prostatic pseudoangiomatous stromal hyperplasia based on histological, immunohistochemical, and electron microscopic findings. The patient was a 74-year-old man with a history of benign prostatic hyperplasia who presented with severe urinary retention and underwent transurethral resection of the prostate. In addition to benign prostatic hyperplasia, the prostate showed areas of irregular spaces lined occasionally by flattened spindle cells in a background of fibrocollagenous stroma. Immunohistochemically, these cells were diffusely positive for vimentin and negative for CD31, CD34, ERG, pancytokeratin, SMA, and D2-40. Electron microscopic findings also showed some cells with fibroblastic features lining these spaces. Given these findings, we postulated that pseudoangiomatous stromal hyperplasia of the prostate has some cells of fibroblastic lineage. Contrary to its breast counterpart where lining cells demonstrate diffusely and strongly positive staining for CD34 and PR, this prostate case showed negative staining for CD34 and PR. These findings indicate potential differences in the histogenesis of prostatic and breast pseudoangiomatous stromal hyperplasia.