Paraneoplastic syndromes are a group of rare disorders that occur when cancer-fighting agents of the immune system attack parts of the brain, spinal cord, peripheral nerves, or muscle. Unlike symptoms caused by the local presence of cancer cells, paraneoplastic syndromes are not related to the direct invasion of the tumor or its metastasis. Instead, these syndromes result from substances produced by the tumor or by an immune response against the tumor.
