Monarch Disease Ontology term MONDO_0003808 (mediastinal extraskeletal osteosarcoma) is an osteosarcoma arising from the mediastinum. Also known as: mediastinal osteogenic sarcoma, mediastinal osteosarcoma, mediastinum osteosarcoma (disease), osteogenic sarcoma of mediastinum, osteogenic sarcoma of the mediastinum, osteosarcoma of mediastinum, osteosarcoma of the mediastinum.