Paraneoplastic syndromes of the nervous system are a group of rare disorders that develop in some people with cancer. Paraneoplastic syndromes of the nervous system occur when cancer-fighting agents of the immune system attack nerve or muscle cells. Cancers commonly associated with these disorders include lung, breast and ovarian cancer. Depending on the location of the cell damage, these syndromes can cause problems with muscle movement or coordination, sensory perception, memory or thinking skills, or sleep. In cases where extensive cell damage has occurred, paraneoplastic syndromes of the nervous system can't be reversed. However, treatment of the underlying cancer and other interventions may prevent further damage, improve symptoms and result in better quality of life.