Case Report: High-grade endometrial adenocarcinoma with somatically derived yolk sac tumor differentiation.

BACKGROUND: Yolk sac tumors (YSTs) arising from somatic tumors of the female genital tract present with variable clinical manifestations depending on the organ of origin. Their diagnosis is highly challenging due to their rarity and the limited number of well-documented cases, and their prognosis remains unclear. The coexistence of high-grade endometrial adenocarcinoma with somatically derived yolk sac tumor differentiation (SDYST) is extremely rare, and evidence-based treatment strategies remain limited. CASE HIGHLIGHTS: A 44-year-old premenopausal woman presented with abnormal uterine bleeding predominantly characterized by menorrhagia for approximately two months. Following surgical staging, pathological examination revealed high-grade endometrial adenocarcinoma with SDYST. Immunohistochemistry (IHC) showed positivity for SALL4 and Glypican-3 (GPC3), with focal expression of alpha-fetoprotein (AFP). Serum AFP levels were markedly elevated. FOLLOW-UP AND OUTCOMES: The patient recovered well postoperatively. After multidisciplinary evaluation, she received BEP-based chemotherapy, and serum AFP levels were dynamically monitored. Serum AFP decreased markedly during treatment, and no definite evidence of disease progression was observed during short-term follow-up. LESSONS: This case provides a practical clinical lesson: markedly elevated serum AFP in an aggressive endometrial tumor should prompt consideration of SDYST, particularly when yolk sac tumor-like morphology and positive immunohistochemical staining for AFP, SALL4, and GPC3 are present. Early recognition of this phenotype may facilitate appropriate immunohistochemical workup, AFP-based disease monitoring, and timely multidisciplinary treatment.