Supplementary Material for: Primary Monophasic Synovial Sarcoma of the Plantar Foot With Pulmonary Metastases in a Young Adult: A Rare Case Report

Abstract
Background:
Synovial sarcoma is a rare, high-grade malignant tumor of mesenchymal origin, accounting for 5–10% of all soft tissue sarcomas. Although it predominantly affects the lower extremities, involvement of the foot is considered uncommon. Diagnosis is often delayed due to its indolent growth, deep anatomical location, and non-specific clinical presentation.
Case presentation:
We report the case of a 28-year-old Arab male smoker who presented with a progressively enlarging, painful soft tissue mass in the plantar aspect of his left foot, associated with swelling and superficial ulcerations. Radiographic evaluation revealed a sub-metatarsal soft tissue mass with preserved bony structures. MRI showed a large, poorly defined lesion infiltrating flexor and extensor tendons, as well as adjacent neurovascular bundles. Chest CT revealed bilateral pulmonary nodules and mass-like consolidations suggestive of metastatic disease. The patient underwent metatarsal-level amputation, and histopathology confirmed a diagnosis of monophasic high-grade synovial sarcoma. He was started on systemic chemotherapy (Ifosfamide, Gemcitabine, and TX), followed by targeted therapy (Pazopanib). Follow-up imaging demonstrated a partial response with reduction in metastatic burden.
Conclusion:
This case illustrates a rare and aggressive presentation of synovial sarcoma arising in the plantar foot, emphasizing the importance of including synovial sarcoma in the differential diagnosis of soft tissue masses in distal extremities. Early imaging, accurate histopathological assessment, and a multidisciplinary treatment approach are essential for optimizing outcomes in such high-grade, metastatic presentations.