High-grade endometrioid carcinoma arising from uterine serosal endometriosis with focal choriocarcinomatous differentiation and embryonal carcinoma-like morphology: a case report and literature review

Abstract Background Malignant transformation of endometriosis is uncommon and most frequently results in endometrioid carcinoma or clear cell carcinoma. Choriocarcinomatous differentiation arising in endometriosis-associated carcinoma is exceptionally rare, and the clinical characteristics and optimal management strategies remain unclear. We report a rare case of high-grade endometrioid carcinoma arising from uterine serosal endometriosis with focal choriocarcinomatous and embryonal carcinoma-like differentiation. Case presentation A 54-year-old postmenopausal woman presented with postmenopausal vaginal bleeding for more than 50 days and rapid enlargement of a pelvic mass. Preoperative serum AFP and CA125 were mildly elevated, whereas serum β-hCG remained persistently below 1 mIU/mL throughout follow-up. After radiological and hysteroscopic evaluation, emergency surgery was performed because of clinical deterioration. A 12-cm pelvic mass invading the sigmoid colon was identified intraoperatively. Histopathological examination demonstrated malignant transformation arising from uterine serosal endometriosis, diagnosed as high-grade endometrioid carcinoma with aberrant p53 immunostaining, accompanied by focal choriocarcinomatous differentiation and focal embryonal carcinoma-like morphology. The patient received five cycles of adjuvant BEP chemotherapy postoperatively. Brain metastasis developed during follow-up and was treated with radiotherapy. Retroperitoneal lymph node metastasis subsequently occurred, and second-line chemotherapy with nab-paclitaxel plus carboplatin was administered. Dynamic serum tumour marker changes correlated with disease burden, whereas serum β-hCG remained negative. Histological confirmation of metastatic lesions was unavailable. Conclusions This case highlights that malignant transformation of postmenopausal uterine serosal endometriosis may rarely exhibit divergent differentiation, including choriocarcinomatous differentiation, despite persistently normal serum β-hCG levels. Aberrant p53 expression may be associated with tumour progression and lineage plasticity, although its biological significance requires further investigation. Individualized multimodal surveillance may be considered for this rare entity, as optimal follow-up strategies remain undefined.