You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is A child 10 yrs of age presents with a mass on his left thigh. The mass seems to be arising from the diaphysis of the femur and involving the soft tissue of the thigh. The child is having fever also. Give your most probable diagnosis - and explain in detail?
Clinical features of Ewing's sarcoma

Similar to any other bone tumor, there may be a history of trauma (often trivial), which brings the tumor into notice.
The child presents with throbbing pain and swelling in mid-shaft (diaphysis).
Swelling may be tender with warmth ness over it.
The tumor is commonest in the shaft' of femur, tibia and humerus.
Generalized illness like fever, together with warm swelling, tenderness and raised ESR may occur and the tumor may be confused with osteomyelitis.