Tazemetostat combined PD-1 inhibitor achieving prolonged survival in primary proximal epithelioid sarcoma: a case report and review of the literature

Background Epithelioid sarcoma (ES) is a rare mesenchymal tumor categorized into proximal (axial) and classical (distal) types. In general, proximal ES come alone with limited treatment options and poor prognosis. Herein, we present the case of a proximal ES treated with a tazemetostat-containing regimen and achieved a favorable response in the third-line setting. Case description A 44-year-old Han woman was noticed a left pelvic floor nodule by computed tomography (CT) scan, and histologically test result confirmed her diagnosis as epithelioid sarcoma (proximal type). Cell staining indicates a negative expression of INI1 but positive expression of PD-L1. Ifosfamide and adriamycin (IA) were introduced as first-line treatment because of multidisciplinary treatment (MDT) of soft-tissue tumor considered tumor invasion is extensive, not eligible to complete surgical resection. Unfortunately, IA was discontinued due to patient intolerance (severe myelosuppression). Anlotinib was used as second-line treatment after rapid disease progression and also discontinued due to vaginal hemorrhage. After the pathology diagnosis, the combination therapy of tislelizumab and tazemetostat was introduced. A significant tumor shrinkage was noticed after 21 months of follow-up, which achieved and continue to maintain a partial response (PR) with further tumor reduction. Conclusions This case first reported a favorable response of primary proximal epithelioid sarcoma treated with EZH2 inhibitor tazemetostat and PD-1 inhibitor tislelizumab, suggesting a potential and well-tolerated treatment regimen for this rare disease.