Case report: Unusual peritoneal spreading by metastatic osteosarcoma of the tibia.

We report a 17-year-old boy with chondroblastic osteosarcoma initially found in left proximal tibia. He received surgical resection and chemotherapy. However, a lung metastasis was found 4 years later. Despite intensive chemotherapy, the metastatic osteosarcoma of lung continued to invade the ribs and later into retroperitoneum and liver. The metastatic pattern of chondroblastic osteosarcoma of tibia directly to the chest and then into the abdomen is unusual.