Tumors that grow from the peripheral nerves can cause an unusual lump, pain, numbness, or even weakness in the area supplied by the nerve in which they arise. They can form anywhere in the body along the peripheral nervous system that links the brain and spinal cord to other parts of the body. Peripheral nerve tumors may be noncancerous (benign peripheral nerve tumors) or cancerous (malignant peripheral nerve tumors). Although most of these tumors are benign, they can lead to nerve damage and loss of muscle control if left untreated. The most common peripheral nerve tumors are schwannomas, and neurofibromas. The tumors may occur sporadically, or they can be caused by a genetic syndrome or predisposition, such as neurofibromatosis and schwannomatosis.