Abstract
Background: Primary retroperitoneal seminoma is an exceedingly rare type of germ cell tumor, accounting for less than 5% of all such tumors. These tumors are typically large at presentation due to their slow growth and the nonspecific nature of symptoms, which often leads to delayed diagnosis. Case Presentation: A 40-year-old male presented with intermittent abdominal pain and a palpable lump in the right paraumbilical region. Ultrasonography revealed a large retroperitoneal mass. Fine needle aspiration cytology confirmed the diagnosis of poorly differentiated malignant tumor, for which he was evaluated with CT-angiogram of the abdomen and FDG PET-CT scans, which showed a large retroperitoneal mass. The patient, then, had a surgical resection of the mass, with postoperative histopathological and immunohistochemical diagnosis of primary retroperitoneal seminoma, and then underwent three cycles of BEP chemotherapy. Scrotal ultrasonography showed no testicular abnormalities, obviating the need for orchiectomy. FDG PET showed a complete response following treatment completion. Postoperative management included routine monitoring of tumor markers and follow-up imaging, which showed a complete response. Conclusion: This case highlights the diagnostic and therapeutic challenges of primary retroperitoneal seminoma. A multidisciplinary approach, including accurate histopathological diagnosis and a combination of chemotherapy and surgery, is essential for optimal management. Early diagnosis and tailored treatment strategies significantly improve patient outcomes.