Abstract Background Extragonadal germ cell tumor (EGCT) is a relatively rare condition, reportedly representing 3–7% of all germ cell tumors. We report a patient who had metachronous testicular tumor with uncommon metastases 20 years after primary retroperitoneal EGCT treatment, along with a corresponding literature review. Case presentation A 49-year-old Japanese man visited our department in November 2017 with chief complaints of indolent right scrotum enlargement and a right inguinal mass. History showed that the patient visited our department of gastroenterology with chief complaints of blackish feces and ill complexion in February 1997. Computed tomography (CT) showed a right retroperitoneal tumor, which was removed in the same month. Histopathological examination showed a teratoma and yolk sac tumor. He was diagnosed with primary retroperitoneal EGCT and received three courses of chemotherapy (bleomycin/etoposide/cisplatin; BEP). Periodic imaging and the determination of tumor markers (alpha-fetoprotein [AFP], human chorionic gonadotropin [HCG], and lactate dehydrogenase [LDH]) showed no recurrence or metastasis during the 5 years postoperatively. Subsequently, he did not visit the outpatient ward. In August 1999, he underwent surgery of right hydrocele. Contrast-enhanced CT showed a 35-mm contrast effect with uneven content in the right testicle and enlarged nodes that raised suspicion for metastases in the right inguinal and right external iliac lymph nodes. All tumor markers were within normal ranges. He underwent right high orchiectomy and resection of the right inguinal lymph nodes in the same month. Histopathological findings revealed seminoma (pT1, pN2, M0, S0, and TNM stage IIB). He received postoperative chemotherapy, one course of BEP therapy, and three courses of etoposide and cisplatin therapy. Post-chemotherapy CT confirmed a complete clinical response at the right external iliac lymph nodes, and this response continued 12 months later. No recurrence or metastasis has been found so far. Conclusions We report a patient in whom a testicular tumor with uncommon metastases occurred 20 years after primary retroperitoneal EGCT treatment. After EGCT treatment, testicular relapses tend to occur after relatively long-term follow-up. After EGCT treatment, such patients must be closely monitored for testicular recurrences and onset of testicular tumor.
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