A benign or malignant soft tissue neoplasm of the mediastinum. Representative examples of benign mediastinal soft tissue neoplasms include chondroma, leiomyoma, lipoma, and rhabdomyoma. Representative examples of malignant mediastinal soft tissue neoplasms include angiosarcoma, leiomyosarcoma, liposarcoma, osteosarcoma, rhabdomyosarcoma, and synovial sarcoma. The disease is mediastinal mesenchymal tumor (Monarch Disease Ontology term MONDO_0003512). Also known as: mediastinal soft tissue neoplasm, mediastinal soft tissue tumor, mediastinal soft tissue tumour, soft tissue neoplasm of mediastinum, soft tissue neoplasm of the mediastinum, soft tissue tumor of mediastinum, soft tissue tumor of the mediastinum, soft tissue tumour of mediastinum.