Explanation
Osteosarcoma, like most bone sarcomas, spreads predominantly via the hematogenous route rather than the lymphatic system. The lungs are the first capillary bed the venous blood encounters, making pulmonary metastases the most common site of initial spread. Approximately 10% to 20% of patients have macroscopic lung metastases at the time of initial diagnosis. Reference: Campbell's Operative Orthopaedics, 14th Edition.