Retroperitoneal choriocarcinoma diagnosed by endoscopic ultrasonography-guided fine needle aspiration biopsy.

A 25-year-old man, with a retroperitoneal bulky mass invading the posterior pancreas head, was referred to investigate and treat his rapidly advancing disease. An endoscopic ultrasonography guided-fine needle aspiration biopsy (EUS-FNAB), performed the next day, and followed by immunostaining for human chorionic gonadotropin (hCG), led to a histological diagnosis of choriocarcinoma. An elevated level of serum hCG also supported the diagnosis. Systemic chemotherapy by etoposide and cisplatin was initiated within a week, with precautions taken to avoid tumour lysis syndrome and choriocarcinoma syndrome. EUS-FNAB enabled a prompt diagnosis and suitable treatment for choriocarcinoma and was considered as an effective diagnostic tool for rare tumours with rapid progression.