Osteosarcoma

A 16-year-old boy presents with a 3-month history of progressive pain and swelling over the distal femur. On examination, there is a firm, tender mass over the distal femur with warmth and overlying skin erythema. The patient reports a history of a minor knee injury 2 months ago. Plain radiographs show a mixed lytic and sclerotic lesion at the distal femoral metaphysis with cortical destruction and a Codman triangle. Serum alkaline phosphatase is elevated at 280 U/L (normal: 30–120). What is the most likely diagnosis?

Which of the following is the most common site of origin for osteosarcoma in the long bones?

What is the most common histological type of osteosarcoma?

A 14-year-old girl with biopsy-confirmed osteosarcoma of the proximal humerus is being staged for treatment. After MRI of the affected limb, which is the most appropriate next investigation to assess for metastatic disease?

Which feature best distinguishes osteosarcoma from Ewing's sarcoma in a 16-year-old boy presenting with a painful metaphyseal lesion of the distal femur?