Metastatic High-Grade Endometrial Stromal Sarcoma With ZC3H7B::BCOR Fusion in Pleural Fluid: A Case Report.
Daniel Lauffenburger, Jan F Silverman
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Case in brief
A 32-year-old woman presented with pelvic pain and a large uterine mass considered suspicious for leiomyosarcoma on MRI; imaging also showed pulmonary and vertebral lesions concerning for metastases. Hysterectomy with bilateral salpingo-oophorectomy established high-grade endometrial stromal sarcoma (HG-ESS), and RNA sequencing identified a ZC3H7B::BCOR fusion. With worsening metastatic disease despite chemoradiation, she developed a large pleural effusion. Cytology showed malignant spindled-to-epithelioid cells in three-dimensional clusters, supporting metastatic HG-ESS when interpreted alongside the primary tumor’s immunophenotype and clinical history.
What made this case unusual
Pleural fluid involvement by HG-ESS is exceptionally uncommon. The effusion also showed a three-dimensional tumor-cell architecture not seen in the primary resection, creating a potential diagnostic pitfall.
Diagnostic / clinical pearl
Metastatic HG-ESS may have cytomorphology that differs from the primary tumor. In pleural fluid, correlate cytologic findings with the patient’s history, prior resection, and tumor immunophenotype.