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 -
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.
Osteosarcoma
Ewing's sarcoma
Chondrosarcoma
Malignant fibrous histiocytoma