Supplementary Material for: A Rare Case of High-Grade Spindle Cell Sarcoma of the Breast: A Case Report

<b><i>Introduction:</i></b> Spindle cell sarcomas are rare breast lesions which are difficult to diagnose due to resemblance with other breast lesions. Histopathological examination and immunohistochemical staining are essential for diagnosis. <b><i>Case Presentation:</i></b> We present a rare case of a 15-year-old female presenting with high-grade rapidly progressive spindle cell sarcoma of the breast, differentiated as phyllodes tumor, with axillary lymph node involvement. Her lesion, on the left breast, measured 16.9 × 10.1 × 13.7 cm. Histology revealed malignant neoplasm arranged in sheets and individual neoplastic cells with an epithelioid to spindled morphology with scant cytoplasm and irregular nuclear membranes. Immunohistochemistry showed weakly positive focal CD-99, and negative WT-1, Myogenin, Desmin, p63, Cytokeratin, Synaptophysin, and CD-34 markers. She was successfully managed with modified radical mastectomy and discharged with regular follow-up advised. <b><i>Conclusion:</i></b> Spindle cell sarcomas have a very aggressive course and prompt diagnosis, and management is mandatory for better patient outcomes. Modified radical mastectomy is the mainstay of treatment.