## Osteosarcoma: Key Distinguishing Features ### Epidemiology & Demographics **Key Point:** Osteosarcoma shows a **male predominance** (approximately 1.5:1 male-to-female ratio), NOT female predominance. Peak incidence occurs in the second decade of life, coinciding with periods of rapid skeletal growth. ### Anatomical Predilection **High-Yield:** Osteosarcoma arises almost exclusively in the **metaphyseal regions** of long bones, with the distal femur and proximal tibia (around the knee) accounting for >50% of cases. Other common sites include the proximal humerus and distal tibia. ### Radiological Features | Feature | Description | |---------|-------------| | **Periosteal reaction** | Sunburst (radiating spicules) or onion-skin (concentric layers) pattern | | **Codman triangle** | Elevated periosteum at the margin of the lesion | | **Mixed lytic/sclerotic** | Ill-defined lesion with both bone destruction and new bone formation | | **Soft tissue mass** | Cortical breakthrough with extraosseous component | ### Metastatic Behavior **Clinical Pearl:** Osteosarcoma is a highly aggressive malignancy with a propensity for **early hematogenous spread**. Pulmonary metastases occur in ~20% of patients at presentation and develop in >80% without treatment. Lung involvement is the most common site of distant spread. ### Histopathology **Key Point:** Malignant spindle cells (osteoblasts) with hyperchromatic nuclei and abnormal mitoses producing osteoid and bone matrix are the hallmark of osteosarcoma. Pleomorphism and high mitotic activity are typical. ### Why Option 1 (Female Predominance) Is Wrong Osteosarcoma shows a **clear male predominance**, making this statement factually incorrect and the correct answer to an "EXCEPT" question.
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