## Most Common Site of Metastasis in Osteosarcoma **Key Point:** The lungs are the most common site of metastasis in osteosarcoma, occurring in 80–90% of patients with metastatic disease at presentation or during follow-up. ### Metastatic Pattern in Osteosarcoma | Metastatic Site | Frequency | Clinical Significance | | --- | --- | --- | | Lungs | 80–90% | Most common; often bilateral | | Bones (other sites) | 5–10% | Skeletal metastases less common | | Liver | 2–5% | Rare; poor prognostic sign | | Brain | <2% | Very rare; late finding | | Lymph nodes | <2% | Uncommon; not typical pattern | ### Pathophysiology Osteosarcoma spreads hematogenously, and the lungs are the first capillary bed encountered after venous drainage from the primary tumor. This explains the high propensity for pulmonary metastasis. **High-Yield:** Approximately 15–20% of patients present with clinically detectable pulmonary metastases at diagnosis. Many more have micrometastases that become apparent during follow-up. ### Clinical Pearl Chest imaging (CT chest) is mandatory at diagnosis and during surveillance. Pulmonary nodules in an osteosarcoma patient are presumed metastatic until proven otherwise. Resection of isolated pulmonary metastases can improve survival in selected cases. ### Mnemonic **"LUNGS First"** — Osteosarcoma metastasizes to the LUNGS first and most often due to hematogenous spread through the venous system. [cite:Harrison 21e Ch 397]
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