15 year old boy presented with a mass in the distal femur. X-ray from the lesion showed features of Codman's triangle and Sunray appearance. The diagnosis is:

Codman's triangle and Sunray appearance are characteristic radiological findings in osteosarcoma. When the tumour elevates the periosteum of bone, a gap occurs between periosteum and bone, where the gap is elevated, bone is formed, creating a triangular shape on radiographs. Ref: Apley's system of ohopaedics and fractures;8th/185; Essential ohopedics by Maheshwari 3rd/219, 222.