A malignant peripheral nerve sheath tumor occurring during adulthood. The disease is adult malignant schwannoma (Monarch Disease Ontology term MONDO_0004545). Also known as: adult MPNST, adult malignant neoplasm of peripheral nerve sheath, adult malignant neoplasm of the peripheral nerve sheath, adult malignant neurilemmoma, adult malignant peripheral nerve sheath neoplasm, adult malignant peripheral nerve sheath tumor, adult malignant peripheral nerve sheath tumour, adult malignant tumor of peripheral nerve sheath.