A paraneoplastic syndrome is a disease or symptom that is the consequence of cancer in the body but, unlike mass effect, is not due to the local presence of cancer cells. These phenomena are mediated by humoral factors (by hormones or cytokines) excreted by tumor cells or by an immune response against the tumor. Paraneoplastic syndromes are typical among middle aged to older patients, and they most commonly present with cancers of the lung, breast, ovaries or lymphatic system (a lymphoma). 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 (such as neuronal proteins), triggering an anti-tumor immune response which may be partially or, rarely, completely effective in suppressing tumor growth and symptoms. 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.
Paraneoplastic syndromes can be divided into four main categories: Endocrine, neurological, mucocutaneous and hematological paraneoplastic syndromes, as well as others that may not fit into any of the above categories:
A particularly devastating form of paraneoplastic syndromes is a group of disorders classified as paraneoplastic neurological disorders (PNDs). These paraneoplastic disorders affect the central or peripheral nervous system; some are degenerative, though others (such as LEMS) may improve with treatment of the condition or the tumour. Symptoms of paraneoplastic neurological disorders may include ataxia (difficulty with walking and balance), dizziness, nystagmus (rapid uncontrolled eye movements), difficulty swallowing, loss of muscle tone, loss of fine motor coordination, slurred speech, memory loss, vision problems, sleep disturbances, dementia, seizures, sensory loss in the limbs.
The most common cancers associated with paraneoplastic neurological disorders are breast, ovarian and lung cancer, but many other cancers can produce paraneoplastic symptoms as well.
Treatment options include:
Therapies to eliminate the underlying cancer such as chemotherapy, radiation and surgery, and
Therapies to reduce or slow neurological degeneration. Rapid diagnosis and treatment are critical for the patient to have the best chance of recovery. Since these disorders are relatively rare, few doctors have seen or treated PNDs. Therefore, it is important that PND patients consult with a specialist with experience in diagnosing and treating paraneoplastic neurological disorders.
^Buckanovich RJ, Posner JB, Darnell RB (1993). "Nova, the paraneoplastic Ri antigen, is homologous to an RNA-binding protein and is specifically expressed in the developing motor system". Neuron11 (4): 657–72. doi:10.1016/0896-6273(93)90077-5. PMID8398153.