This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Osteogenic Sarcoma, Subject name: Orthopaedics
[{'content': "Swelling over distal end of femur with secondaries in lungs, diagnosis is: \nSelect and explain. \nA. Osteogenic sarcoma, B. Giant cell tumor, C. Osteoclastoma, D. Ewing's sarcoma", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' ie Osteogenic sarcoma Osteosarcoma are aggressive lesion and metastasize widely through the blood stream; usually first to the lungs.Ewing's sarcoma also metastasizes, to lung & bones. Bone to bone metastasis are more commonOsteoclastoma rarely metastasizes.Thus this lesion could be either osteosarcoma or Ewing's sarcoma but osteosarcoma would produce swelling at distal end of femur (b/c it arises from metaphysis) and Ewing would not be placed distally b/c it arises from the diaphysis.", 'role': 'assistant'}]