Supplementary Material for: Case Report of Giant Myxoid Fibrosarcomatous Dermatofibrosarcoma Protuberans Compressing the Right Jugular Vein: A Multidisciplinary Approach to Complex Surgical Management

Introduction: Dermatofibrosarcoma protuberans (DFSP) is a slow-growing cutaneous neoplasm with high cure rates following complete surgical resection. However, 5-15% of classic DFSP cases undergo fibrosarcomatous transformation, resulting in fibrosarcomatous DFSP (FS-DFSP), a more aggressive variant with significantly higher rates of local recurrence, metastasis, and mortality. This case presents a rare myxoid variant of FS-DFSP with complex anatomical involvement requiring multidisciplinary management.

Case Presentation: A 56-year-old female presented with a giant recurrent chest mass measuring 15 × 12 × 6 cm, initially misdiagnosed as fibroma 19 years prior. Advanced imaging revealed an 8 × 13 × 12 cm poorly defined soft tissue mass involving the pectoralis major and extending to the sternocleidomastoid muscles, with compression of the proximal right jugular vein. Histopathological examination confirmed FS-DFSP with myxoid differentiation, characterized by diffuse spindle cell infiltration in a herringbone pattern. Immunohistochemistry revealed CD34+, EMA+, and Actin+ staining with negative desmin, S100, and STAT-6. COL1A1-FISH analysis demonstrated COL1A1/PDGFB fusion in 8% of cells. Management included tumor vascular embolization, surgical resection with 3 cm margins, skin grafting, local flap repair, and adjuvant radiation therapy due to anatomical constraints and residual tumor involvement of the anterior sternum.

Conclusion: This case highlights the myxoid variant of FS-DFSP, emphasizing the importance of comprehensive histopathological evaluation, multidisciplinary treatment planning, and long-term surveillance. The successful management with combined surgical and radiation therapy demonstrates the need for individualized treatment approaches in complex anatomical locations. Four-year follow-up shows no evidence of recurrence, supporting the efficacy of aggressive multimodal therapy in preventing local recurrence in FS-DFSP.