Sclerosing Rhabdomyosarcoma Arising in Desmoid Fibromatosis 17 Years After Therapeutic Radiation

Case: A 54-year-old man received radiation therapy (50 Gy) for popliteal desmoid fibromatosis. After 17 years, he developed an enlarging mass in the same location. Initial biopsy suggested recurrent desmoid, but a repeat biopsy revealed sclerosing rhabdomyosarcoma. Despite chemotherapy and transfemoral amputation, he developed pulmonary and chest wall metastases. Conclusion: The 17-year latency period and tumor location within the prior radiation field are consistent with radiation-associated malignant transformation; however, definitive causality cannot be established. Orthopaedic surgeons should maintain a low threshold for rebiopsy of any new or changing mass in previously irradiated fields.