A 15-year-old boy presents with pain and swelling around the knee. X-ray shows a destructive lesion in the distal femoral metaphysis with periosteal elevation forming a triangular shadow at the margins. Biopsy shows a highly malignant spindle cell tumor producing osteoid directly from tumor cells. The most common site of distant metastasis is:
- A Regional lymph nodes
- B Liver
- C Lung ✓
- D Brain
Correct answer: C. Lung
Explanation
The description is classic for osteosarcoma (osteogenic sarcoma), the most common primary malignant bone tumor in adolescents. It arises preferentially in the metaphysis of long bones around the knee (distal femur, proximal tibia). The Codman triangle on X-ray results from periosteal elevation by the expanding tumor. Osteosarcoma disseminates hematogenously, with the lung being the primary and most common site of metastasis, determining prognosis. Lymph node metastasis is uncommon.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.