Serous endometrial cancer with an elusive preoperative diagnosis

Uterine serous carcinoma (USC) is an aggressive histological subtype of endometrial cancer that frequently presents with early extrauterine spread, often without uterine symptoms. We report a diagnostically challenging case of a postmenopausal woman presenting with malignant ascites, peritoneal metastases and deep vein thrombosis, but no abnormal uterine bleeding. Preoperative imaging and biopsies were inconclusive, suggesting a possible leiomyoma or ovarian malignancy. Exploratory laparotomy revealed widespread peritoneal disease, and histopathology demonstrated serous carcinoma confined to an endometrial polyp with lymphovascular space invasion but no myometrial invasion. Immunohistochemistry showed p53 and p16 positivity, focal WT1 (Wilms tumor 1 protein) positivity, weak ER (estrogen receptor) expression and MMR (mismatch repair) proficiency, confirming primary USC (International Federation of Gynaecology and Obstetrics (FIGO) stage IVB). The patient was initiated on paclitaxel-carboplatin chemotherapy. This case highlights the diagnostic difficulties of USC, its potential to mimic ovarian carcinoma and the importance of integrating surgical, pathological and molecular evaluation for accurate diagnosis and management.