Pseudoangiomatous Stromal Hyperplasia-Like Change in Mixed Epithelial and Stromal Tumor of the Seminal Vesicle: A Case Report Expanding the Morphologic Spectrum With 19-Year Follow-Up

Mixed epithelial and stromal tumor (MEST) of the seminal vesicle is a rare biphasic neoplasm whose stromal component, while morphologically diverse, has not previously been reported to exhibit pseudoangiomatous stromal hyperplasia (PASH)-like change. We report a low-grade seminal vesicle MEST in a 70-year-old man in whom transrectal needle biopsy demonstrated prominent interanastomosing slit-like spaces within keloid-like collagen lined by bland spindle cells, without intraluminal erythrocytes-a pattern that raised concern for a vascular or sarcomatous neoplasm before the biphasic architecture was fully appreciated on the resection specimen. Immunohistochemically, the spindle cells showed a CD34+/CD31-/ERG- phenotype, supporting a myofibroblastic pseudovascular process rather than true endothelial differentiation. The patient remained recurrence-free for 19 years after complete excision. This observation expands the morphologic spectrum of seminal vesicle MEST and highlights a practical diagnostic challenge in biopsy interpretation. Recognition of PASH-like change, supported by targeted immunohistochemical evaluation, can help resolve the differential diagnosis and avoid overgrading in biopsy-limited settings.