A classification for rare disorders of diverse organ systems (endocrine, neuromuscular, gastrointestinal, renal, dermatologic, rheumatologic, hematologic) that are affected by substances secreted by a distant neoplasm but not by the action of the neoplasm itself metastasizing to that organ or tissue. Less than 1 % of neoplasms are associated with these syndromes. An immune-mediated response to neoplasm-elaborated proteins may be the cause of these syndromes. Additionally, their manifestation may signal the presence of an occult neoplasm, potentially at an earlier stage of disease thereby leading to a better clinical outcome. Constitutional signs may include fever, night sweats, anorexia and cachexia. Clinical course is usually progressive. Prognosis is variable depending on the effective treatment of the underlying neoplasm.