Paraneoplastic syndromes are a heterogeneous group of disorders caused by an abnormal immune response to a neoplasm. The substances produced are not due to the direct effect of the tumor, such as metastasis, mass effect, or invasion. Antibodies, hormones, cytokines, and other substances are generated and affect multiple organ systems. About 10% of cases of cancer are affected by paraneoplastic syndromes. The common cancers that present with paraneoplastic syndromes include cancer of the lung, breast, ovaries, kidney, liver, and stomach and lymphomas.