Every nerve in your body is protected by a layer of tissue called a sheath. A schwannoma is a tumor that grows in the sheaths of nerves in your peripheral nervous system, or the parts of your nervous system that aren’t in your brain or spinal cord. You may hear schwannomas referred to as neurilemomas, neuromas,or neurolemomas. Schwannomas are usually benign, meaning they’re harmless. In rare cases, they can be malignant, or cancerous. Malignant schwannomas are also called soft tissue sarcomas. Most people with schwannomas only have one, but it’s possible to have more. Multiple schwannomas are usually a result of schwannomatosis. This is the least common type of a rare condition called neurofibromatosis, a genetic disorder that causes tumors in the nervous system. Another form, called neurofibromatosis type 2 (NF2), can also cause schwannomas.