A 35-year-old man with an intra-abdominal testicular tumor arising from the right unresolved intraabdominal testis is reported. At 10 years old, left orchidopexy was successfully performed for bilateral undescended testes. However, the right testis was not detected during the operation, and it was diagnosed as vanishing testis. Twenty-five years later, he was referred to our hospital with the complaint of right lower abdominal pain. Computed tomography revealed huge pelvic tumors and bulky para-aortic lymph node swellings. Histopathologic examination of the needle biopsy specimen obtained from the pelvic tumor revealed seminomatous germ cell tumor. Taking the results with a tumor marker study into consideration, the patient was tentatively diagnosed with non-seminomatous germ cell tumor NSGCT (stage IIB) arising from the unresolved intra-abdominal testis or extragonadal germ cell tumor. He received 3 courses of bleomycin, etoposide, cisplatin (BEP), and 4 courses of VP-16, ifosfamide, cisplatin (VIP). After chemotherapy, we performed tumorectomy and retroperitoneal lymphadenectomy because tumor markers were normalized and 2-[18F] fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)-CT revealed normalization. We identified the pelvic tumor as an intra-abdominal testicular tumor arising from right unresolved intra-abdominal testis. Pathological examination revealed no residual tumor cells. There has been no recurrence 17 months after surgery
