Paraneoplastic syndrome

A paraneoplastic syndrome is a syndrome (a set of signs and symptoms) that is the consequence of a tumor in the body (usually a cancerous one).^[1] It is specifically due to the production of chemical signaling molecules (such as hormones or cytokines) by tumor cells or by an immune response against the tumor.^[2] Unlike a mass effect, it is not due to the local presence of cancer cells.^[3]

Paraneoplastic syndromes are typical among middle-aged to older people, and they most commonly occur with cancers of the lung, breast, ovaries or lymphatic system (a lymphoma).^[4] Sometimes, the symptoms of paraneoplastic syndromes show before the diagnosis of a malignancy, which has been hypothesized to relate to the disease pathogenesis. In this paradigm, tumor cells express tissue-restricted antigens (e.g., neuronal proteins), triggering an anti-tumor immune response which may be partially or, rarely, completely effective^[5] in suppressing tumor growth and symptoms.^[6][7] Patients then come to clinical attention when this tumor immune response breaks immune tolerance and begins to attack the normal tissue expressing that (e.g., neuronal) protein.

The abbreviation PNS is sometimes used for paraneoplastic syndrome, although it is used more often to refer to the peripheral nervous system.