S2896 A Rare Case of Necrotic Testicular Seminoma Presenting as a Large Retroperitoneal Mass Diagnosed With EUS and Laparotomy

Introduction: Retroperitoneal seminomas are a rare form of cancer that accounts for approximately 2% of all seminomas. Seminomas commonly present with fever, weight loss, abdominal or back pain, and a painless testicular nodule. The differential diagnosis for a retroperitoneal mass is broad, including abscess, lymphoma, sarcoma, metastatic lymph nodes, and extragonadal tumors. The pathogenesis of germ cell tumors is unclear, but the failure of primordial germ cell migration during embryonal development has been suggested. We report an atypical case of a large necrotic retroperitoneal mass diagnosed as a primary retroperitoneal seminoma after EUS and laparotomy. Case Description/Methods: A 33-year-old male with no medical history presented to the ED for new-onset flank pain and night sweats. On admission, the patient was febrile and tachycardic. The testicular exam and US of the testes were normal. CT abdomen and pelvis revealed a well-circumscribed, round mass posterior to the pancreatic head. EUS with FNA was performed, noting a round heterogenous 7.1cm x 6.2cm mass with well-defined borders and a necrotic center located posterior to the pancreatic head. An intact interface was seen between the mass and the duodenum, IVC, pancreas, and right kidney, suggesting a lack of invasion. The FNA yielded 0.5ml of blood-tinged, thick, and purulent fluid with cytology significant for malignant tumors with extensive necrosis. An exploratory laparotomy with excisional biopsy established the diagnosis of extragonadal germ cell tumor with extensive necrosis, consistent with seminoma. The patient completed four cycles of Etoposide followed by a right-sided orchiectomy for residual lesions found on the right testicle. A post-surgical PET scan did not demonstrate recurrence. Discussion: Primary retroperitoneal seminoma is a rare entity that must be considered when evaluating a retroperitoneal mass. GCTs are the most common neoplasm arising from the testes, with < 2% originating in other locations, termed primary extragonadal GCTs. Studies suggest the remission rate with chemotherapy and resection of residual masses was 92%, and the five-year overall survival rate was 88% for primary retroperitoneal tumors. Early identification of primary retroperitoneal seminomas may expand therapeutic possibilities and help improve outcomes for patients with a favorable prognosis. EUS-FNA was attempted in this case to obtain the diagnosis; however, an excisional biopsy was required to confirm the diagnosis.