A 16-year-old boy presents with progressive pain and swelling around the knee for 3 months. Radiographs show a mixed lytic-sclerotic lesion in the distal femur with cortical destruction and a Codman triangle. Biopsy confirms osteosarcoma. Which of the following is NOT a characteristic feature of osteosarcoma?

## Characteristic Features of Osteosarcoma **Key Point:** Osteosarcoma is the most common primary malignant bone tumor in children and adolescents, with a male predominance (not female), arising in the metaphyseal regions of rapidly growing long bones. ### Epidemiology & Demographics - **Age of onset:** 10–25 years (peak during growth spurt) - **Sex predilection:** **Males > females** (approximately 1.5:1 ratio) - **Most common sites:** Around the knee (50–60%) — distal femur and proximal tibia - Other sites: proximal humerus, pelvis, jaw ### Pathological Features | Feature | Details | |---------|----------| | **Location** | Metaphyseal region of long bones (area of rapid bone growth) | | **Histology** | Malignant spindle cells producing osteoid/bone (diagnostic) | | **Radiographic signs** | Codman triangle, sunburst pattern, cortical destruction | | **Presentation** | Pain, swelling, pathological fracture (10–15% of cases) | **High-Yield:** The metaphyseal location in the region of maximum longitudinal growth is a hallmark — osteosarcoma arises where bone growth is fastest. ### Metastatic Behavior - **Lungs** are the most common site of metastasis (80–90% of disseminated disease) - Hematogenous spread is the primary route - Pulmonary metastases may be present at diagnosis in ~20% of cases **Clinical Pearl:** Chest imaging (CT) is mandatory at diagnosis to exclude pulmonary metastases, as their presence significantly impacts prognosis and treatment planning. ### Why the Distractor is Wrong The option stating "arises in females over males" is **factually incorrect**. Osteosarcoma shows a clear **male predominance**, not female. This is a classic NEET PG trap — reversing a well-known epidemiological fact. --- ## Summary Table: Osteosarcoma vs Other Bone Tumors | Tumor | Age | Sex | Location | Metastasis | |-------|-----|-----|----------|------------| | **Osteosarcoma** | 10–25 | M > F | Metaphysis (knee) | Lungs | | Ewing sarcoma | 10–20 | M > F | Diaphysis/metadiaphysis | Lungs, bone | | Giant cell tumor | 20–40 | F = M | Epiphysis (knee) | Rare | | Chondrosarcoma | 40–60 | M = F | Pelvis, femur | Lungs |