History: 55 year old male with left flank mass on physical exam.
The diagnosis in this case was metastatic extraskeletal osteosarcoma, which is a malignant mesenchymal soft tissue tumor that contains components of cartilage, bone, and osteoid. Unfortunately, these tumors have a poor prognosis, with an approximately 25% 5 year survival rate. Notice the pleural effusions in the patient above, which may be malignant effusions. Extraskeletal osteosarcomas may be associated with prior trauma or radiotherapy.