Case Report: Recurrent pelvic gestational choriocarcinoma arising from an occult complete mole unmasked by short tandem repeat genotyping.

Background: Pelvic gestational choriocarcinoma (GCC) is very rare. It may mimic ectopic pregnancy because of the elevated human chorionic gonadotropin (hCG) levels and absence of typical uterine lesions. After choriocarcinoma is identified, accurate determination of tumor origin is critical for prognostic risk stratification and treatment selection. Case presentation: A 29-year-old woman presented with irregular vaginal bleeding and markedly rising hCG levels, with imaging revealing a pelvic mass, and was initially diagnosed with ectopic pregnancy. Emergency laparoscopy and pathological review confirmed choriocarcinoma, but the resected tissue was insufficient for short tandem repeat (STR) genotyping to determine the tumor origin. Based on her pregnancy history and age, she was empirically treated for presumed GCC and achieved complete remission after chemotherapy. Approximately 3 years later, she developed an isolated recurrence at the same location. She then underwent three-dimensional laparoscopic resection, which enabled STR genotyping. The analysis revealed a homozygous androgenetic diploid pattern, definitively confirming gestational origin and establishing the causative gestation as a complete hydatidiform mole, thereby revising the prognostic score from 9 to 8. Postoperatively, the patient received five cycles of chemotherapy, serum hCG normalized, and she remains disease-free at 25 months of follow-up. Conclusions: The case underscores two key messages. First, STR genotyping is highly valuable for accurate etiological classification and risk stratification in extrauterine choriocarcinoma. Second, surgical resection of an isolated chemoresistant or recurrent lesion, even at elevated hCG levels, can provide essential tissue for molecular diagnosis and facilitate rapid biochemical remission.