Osteosarcoma involving distal femur in a 14 y/o male. The plain film shows an ill-defined sclerotic lesion in the distal metaphysis of the femur. It is associated with sunburst type periosteal reaction (on the left) and a large soft tissue mass on the right. The tumor has breached the epiphyseal plate. Histopathologic examination revealed an osteoblastic osteosarcoma.