High-Grade Angiosarcoma Transformation in Schwannoma and SMARCB1 Mutation: A Case Report.

BACKGROUND Epithelioid angiosarcoma arising in a schwannoma is an exceedingly rare and aggressive malignancy, with less than 25 cases reported in the English-language literature. Histopathologically, it combines the spindle cell characteristics of schwannomas with the epithelioid, vascular nature of angiosarcomas. The presence of SMARCB1 frameshift loss-of-function (LOF) mutations impairs gene function, contributing to various aggressive cancers. CASE REPORT A 58-year-old man presented with slow-growing masses on the back and arm. Ultrasound and MRI findings were suspicious for nerve sheath tumor. He underwent surgical resection and biopsy, with results revealing SOX10-positive, S100-positive, CD31-positive, excisional margins-positive characteristics of high-grade epithelioid angiosarcoma arising in a schwannoma. A PET scan suggested metastasis to intrathoracic lymph nodes. Tempus molecular profiling showed SMARCB1 frameshift LOF. He was treated with weekly paclitaxel and tazemetostat, with slight improvement in pain; however, he developed symptomatic disease progression. Due to extensive metastatic disease precluding surgical resection, palliative radiation was added to the systemic treatment regimen. After several cycles of treatments with worsening symptoms, he decided to enter hospice care. CONCLUSIONS Presentation of high-grade angiosarcoma arising in schwannoma can be non-specific, posing a diagnostic challenge. Histopathology and immunohistochemistry are essential in the diagnosis and may be characterized by the presence of SMARCB1 frameshift LOF as a prognostic biomarker. Surgical resection with negative margins is the cornerstone of treatment supplemented by chemotherapy and radiotherapy. Patients should be monitored closely for recurrence or metastasis.