Case Report: Primary non-gestational small intestinal choriocarcinoma misdiagnosed as ectopic pregnancy.

Background: Primary small intestinal choriocarcinoma is an extremely rare nongestational malignancy associated with non-specific clinical manifestations and a high risk of misdiagnosis. Case presentation: A 40-year-old female presented with amenorrhea, vaginal bleeding, and elevated serum β-human chorionic gonadotropin (β-hCG). She was initially suspected of ectopic pregnancy and received emergency laparoscopic exploration. A 2×1 cm ileal tumor was resected, and histopathological testing verified choriocarcinoma. Given the intraoperatively normal pelvic viscera and postoperative imaging ruling out alternative primary tumors, primary small intestinal choriocarcinoma was confirmed. The patient attained complete biochemical remission after five cycles of FAV chemotherapy (fluorouracil, actinomycin D, vincristine), with serum β-hCG levels falling from 1336 mIU/mL to 0.23 mIU/mL. Thirteen months after FAV completion, biochemical relapse emerged, accompanied by pulmonary and right adnexal metastatic lesions. The adnexal lesion developed chemoresistance following nine cycles of EMA-CO (etoposide, methotrexate, actinomycin D, cyclophosphamide, vincristine) and only showed minimal response to two cycles of FAEV (fluorouracil, actinomycin D, etoposide, vincristine). Subsequent right adnexectomy was conducted, followed by two consolidation cycles of FAEV, which resulted in durable long-term remission. Conclusion: This case highlights a diagnostic pitfall in gynecological practice and suggests that multimodal therapy combining chemotherapy and surgery may achieve long-term disease control in refractory cases. Given the rarity of primary small intestinal choriocarcinoma, further molecular data are needed to validate these findings and refine therapeutic strategies.