Synchronous primary cancers involving the endometrium and fallopian tube: A case report.

The co-occurrence of uterine and adnexal malignancies poses significant diagnostic challenges in distinguishing synchronous primary tumors from metastatic lesions. This study presents a rare case of concurrent dedifferentiated endometrial carcinoma (DEC) and high-grade serous tubal carcinoma and highlights the critical role of integrated pathological and molecular analyses. A 58-year-old woman presented with a 2-month history of irregular vaginal bleeding. Transvaginal ultrasound demonstrated endometrial thickening (1 cm) with intrauterine fluid accumulation. Hysteroscopic biopsy confirmed endometrioid adenocarcinoma. The patient underwent laparoscopic radical hysterectomy with bilateral adnexectomy and pelvic lymphadenectomy. Histopathological examination identified two distinct neoplasms: (1) DEC (microsatellite instability-high subtype) located at the left uterine fundus and (2) High-grade serous carcinoma (SET subtype: solid, endometrioid-like, transitional patterns) in the right fallopian tube. Following surgery, six cycles of adjuvant chemotherapy with TP regimen (liposomal paclitaxel plus carboplatin) were administered. The patient remains disease-free at a 46-month follow-up. This case underscores the diagnostic complexity of synchronous gynecological malignancies. Comprehensive immunohistochemistry combined with molecular characterization is essential for accurate tumor classification, which directly determines staging precision and therapeutic decision-making. The favorable long-term outcome in this case suggests potential clinical implications for dual primary management strategies.