Abstract
BACKGROUND: Mixed epithelial and stromal tumors (MESTs) of the seminal vesicle are exceptionally rare neoplasms composed of both epithelial and stromal elements, posing significant diagnostic challenges due to their rarity and overlapping characteristics with other pelvic neoplasms. CASE PRESENTATION: We describe a 45-year-old patient with chronic pelvic pain and obstructive urinary symptoms. Imaging revealed a large cystic and solid mass involving his seminal vesicles, with significant mass effect on adjacent structures. Differential diagnoses included seminal vesicle adenocarcinoma and sarcoma. Complete surgical resection and subsequent histopathological analysis confirmed a low-grade seminal vesicle MEST with biphasic epithelial and stromal components, lacking atypia or notable mitotic activity. Immunohistochemical analysis revealed stromal positivity for estrogen receptor (ER), progesterone receptor (PR), smooth muscle actin, desmin, and CD34, and epithelial positivity for PAX8, PAX2, CK7, and MUC-6, supporting the diagnosis. The patient remains disease-free 32 months post-surgery. CONCLUSION: Seminal vesicle MESTs are rare and histologically diverse tumors, with pathogenesis likely hormonally influenced given ER and PR expression. Diagnosis requires a multidisciplinary approach, including imaging, histopathology, and immunohistochemistry. Surgical excision is the preferred treatment, offering an excellent prognosis for low-grade cases. This case emphasizes the importance of detailed documentation to improve understanding and management of these rare tumors, and its prognosis.