This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Radiotherapy is the treatment of choice in the following malignancy: 
Select and explain. 
A. Ewing's sarcoma, B. Osteosarcoma, C. Osteoclastoma, D. Synol sarcoma
A: Ewing's sarcoma
Answer: A: Ewing's sarcoma 
Explanation: Ewing sarcoma is a small blue cell tumor with a characteristic t(11:22) chromosomal translocation. It commonly occurs in children older than 5 years and in young adults. The pelvis, knee, proximal humerus, and femur diaphysis are the most common locations. The classic "onionskin" appearance of multiple layers of reactive periosteum is seen. Ewing sarcoma is very radiosensitive; often, when surgical resection is not an option or positive margins remain, consolidative radiation therapy is used. Ref: Conley A, Park M.S., Trent J.C., Patel S (2011). Chapter 40. Soft Tissue and Bone Sarcomas. In Kantarjian H.M., Wolff R.A., Koller C.A. (Eds), The MD Anderson Manual of Medical Oncology, 2e.