RESUMEN
Malignant tumors of the seminal vesicles are rare; they may be of epithelial or mesenchymal origin. Carcinomas are the most common and pelvic sarcoma may be confused with a primary tumor of the seminal vesicles. Little is known of the prognosis and best sequence of treatment in such sarcoma. We report a rare case of extra-skeletal Ewing sarcoma/primitive neuroectodermal tumor of the seminal vesicles in a 54-year-old man who presented with chronic lower abdominal pain, urinary retention, and severe constipation. Pelvic CT scan and MRI confirmed the presence of a soft tissue mass lesion centered on seminal vesicles. A trans-gluteal Tru-cut biopsy confirmed the diagnosis. Three cycles of the preoperative chemotherapy VAC/IE (vincristine, Adriamycin and cyclophosphamide, followed by ifosfamide and etoposide) protocol achieved an excellent clinical response.