Paraneoplastic Syndromes

NEUROLOGICAL REVIEW Paraneoplastic Syndromes

Josep O. Dalmau, MD, PhD; Jerome B. Posner, MD

he fact that a small cancer hidden in the chest, abdomen, or pelvis could destroy or damage portions of the nervous system, such as cerebellar Purkinje cells or cholinergic synapses, has intrigued neurologists since paraneoplastic syndromes were first described. In 1965, when little was known about their pathogenesis, a full issue of the Tjournal Brain and an international symposium were devoted to paraneoplastic disorders. In this decade, the discovery of several paraneoplastic antibodies that react with both the nervous system and the causal cancer has rekindled interest in these syndromes (Table). Several other factors make these rare syndromes of clinical and scientific interest. A recent review by Dalmau and Posner1 contains a more comprehensive bibliography of paraneoplastic syndromes. These disorders challenge the diagnostic both patients, cancer of the breast was skills of the neurologist. The patient’s can- subsequently discovered. The anti-Ta an- cer has usually not yet been discovered tibody seems to be specific for testicular and, because other inflammatory disor- cancer. ders of the nervous system can mimic para- Paraneoplastic syndromes are a thera- neoplastic syndromes, the diagnosis is of- peutic challenge for the neurologist. With ten difficult. However, paraneoplastic the exception of myasthenia gravis, the antibodies, in most (but not all) in- Lambert-Eaton myasthenic syndrome, neu- stances, unequivocally establish that the romyotonia, dermatomyositis, and cer- disorder is paraneoplastic. tain peripheral neuropathies associated with The disorders challenge the diagnos- myeloma, treatment of paraneoplastic syn- tic skills of the oncologist. The underly- dromes is generally unsatisfactory. ing cancer may be so small as to be unde- Paraneoplastic syndromes are a thera- tectable by even the most sophisticated peutic challenge for the oncologist. Sub- imaging techniques. Fortunately, many stantial evidence suggests that in patients paraneoplastic antibodies also point to the with paraneoplastic antibody-positive se- most likely underlying tumor. For ex- rology, the neoplasms grow more indo- ample, the anti-Hu antibody indicates the lently and are less likely to metastasize than presence of a small cell lung cancer and in patients with the same cancer who are the anti-Yo antibody, the presence of an not antibody positive or who do not have ovarian or breast cancer. So strong is the paraneoplastic symptoms.2 Recent animal association of the anti-Yo antibody with data support these conclusions.3 If the neu- gynecologic cancers that we and others rec- rologist chooses to treat the neurologic ommend hysterectomy and salpingo- symptoms with immune suppression, it is oophorectomy in anti-Yo–positive post- possible that the oncologist will be faced menopausal patients with normal with a more rapidly growing tumor. mammograms, even in the absence of posi- Paraneoplastic antibodies react with tive imaging studies of the pelvis. In only both the cancer and the nervous system. 2 patients of whom we are aware has a can- These antibodies identify antigens, pres- cer not been found at pelvic surgery. In ent normally only in the nervous system (usually in neurons), but for uncertain rea- From the Department of Neurology, Memorial Sloan-Kettering Cancer Center, New sons expressed ectopically in certain tu- York, NY. mors. The immune system recognizes the

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Onconeuronal Antibody Associated Cancer Syndrome Antigen Antigen Anti-Hu SCLC and neuroblastoma Encephalomyelitis, sensory neuronopathy All neuronal nuclei, 35-40 kd HuD, HuC, and Hel-N1 Anti-Yo Gynecologic and breast Cerebellar degeneration Cytoplasm Purkinje cells, CDR34, CDR62-1, 34 and 62 kd and CDR62-2 Anti-Ri Breast, gynecologic, Cerebellar ataxia, opsoclonus Neuronal nuclei CNS, NOVA1 and NOVA2 and SCLC 55 and 80 kd Antiamphiphysin Breast Stiff-man, encephalomyelitis Synaptic vesicles, 128 kd Amphiphysin

Anti-VGCC SCLC Lambert-Eaton myasthenic syndrome Presynaptic VGCC ␣1-Subunit Anti-MysB SCLC Lambert-Eaton myasthenic syndrome Presynaptic VGCC ␤-Subunit VGCC Anti-Ma Multiple Cerebellar, brainstem dysfunction Neuronal nuclei and cytoplasm, Ma1 and Ma2 37 and 40 kd Anti-Ta Testicular Limbic encephalitis, brainstem dysfunction Neuronal nuclei and cytoplasm, 40 kd Ma2 Anti-Tr Hodgkin lymphoma Cerebellar degeneration Cytoplasm neurons, Purkinje cells, In progress and spiny dendrites Anti-CAR SCLC and others Photoreceptor degeneration Retinal photoreceptor, 23 kd Recoverin Anti-CV2 SCLC and others Encephalomyelitis, cerebellar degeneration Glia (subset), 66 kd POP66

*Data modified from Dalmau and Posner.1 SCLC indicates small cell lung cancer; CNS, central nervous system; VGCC, voltage-gated calcium channels; and CAR, carcinoma-associated retinopathy.

proteins expressed by the tumor as foreign and mounts acute sensory neuronopathy associated with lung can- an immune attack that partially controls tumor growth cer had in their serum a low-titer antibody that reacted (in some instances it appears to destroy the tumor so that with the cytoplasm [sic] of neurons in the guinea pig ce- no tumor is found even at autopsy). The immune reac- rebral cortex. No additional information was forthcom- tion also attacks portions of the nervous system that ex- ing until 1985, when Graus and colleagues7 described first press the antigen. The pathogenesis of some syndromes 2 and later 4 patients with subacute sensory neuropathy (myasthenia gravis, Lambert-Eaton myasthenic syn- associated with small cell lung cancer who had in their drome, neuromyotonia) is mediated by antibodies but, serum high titers of a complement-fixing antibody that for the majority of antibody-associated paraneoplastic syn- reacted predominantly with the nuclei of central and pe- dromes of the central nervous system (CNS), the major ripheral nervous system neurons. The Hu antigens cor- pathogenic mechanism appears to be related to cyto- respond to a set of proteins of 35 to 40 kd on Western toxic T-cell responses.4 blot using either neuronal or small cell lung cancer pro- In paraneoplastic syndromes affecting the CNS, in- tein extracts. Subsequently, it has become evident that flammatory infiltrates of T cells and plasma cells are found the anti-Hu antibody is a marker not only of sensory both in the nervous system and in the cancer. Further- neuronopathy but also of encephalomyelitis. more, IgG normally absent from the CNS can be found Subsequent work has identified several proteins be- not only within the neuropil but also within neurons. Elu- longing to the Hu family. All of these have high homol- tion studies indicate that the antibody found in the brain ogy with the Drosophila embryonic lethal abnormal vi- and the tumors of patients with paraneoplastic syn- sual (ELAV) protein, necessary for the development of dromes is the same antibody that reacts with onconeu- the eye and the CNS of the fly. All Hu proteins, includ- ral antigens.5 ing HuD, HuC, Hel-N1, and HuR, contain 2 tandem RNA Because onconeural antigens are normally present recognition motifs (RRM), a basic domain, and a third only in neurons, it is likely that they are important for neu- RRM. The basic domains of HuD, Hel-N1, and HuC are ral development and phenotype maintenance. Accord- alternatively spliced yielding HuDpro, HuDmex, Hel- ingly, we and others have used paraneoplastic antibodies N2, and HuC isoforms. The expression of HuD, HuC, and to probe complementary DNA expression libraries to clone Hel-N1 is restricted to neurons, but HuR is reported to the antigen(s) identified by these antibodies (Table). With be ubiquitously expressed in extraneuronal tissues.8 These respect to those antigens that have been identified so far, proteins bind to AU-rich elements, which are present in the molecular analysis appears to confirm that onconeu- the 3Ј-untranslated region of messenger RNA (mRNA), ral antigens are important to neuronal function. The re- that regulate cell proliferation (ie, c-fos, c-Myc, Gap43, mainder of this article will address the question of the func- and GM-CSF). The exact function of the Hu proteins re- tion of some onconeural antigens. mains unknown, but it has been postulated that they act as transfactors involved in selective mRNA degradation. Hu ANTIGENS The anti-Hu antibodies bind to the first and second RRM of HuD, HuC, and Hel-N1 but not HuR; it is un- The term Hu antigens refers to a family of nuclear pro- known how the binding of anti-Hu antibodies may af- teins normally expressed in all neurons of the central and fect the function of these proteins, but for HuD the first peripheral nervous system but not in other cell types (with and second RRM are essential for RNA binding. the possible exception of the testes). The antigen was prob- Although a study of the developing mouse nervous ably first identified by Wilkinson and Zeromski6 in 1965, system has demonstrated a hierarchy of expression of the when they reported that 4 patients suffering from sub- Hu proteins, in the adult mouse, all Hu proteins appear

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©1999 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 to be expressed in most brain regions.9 The same study cho et al,13 is a 34-kd protein that consists of 34 inexact showed that dorsal root ganglia, which in about 70% of tandem repeats of a hexapeptide. Amino acids 2, 3, 4, and patients with the anti-Hu syndrome is the initial target 6 in this hexapeptide are invariably leucine, glutamate, of the disease, has a robust expression of the 4 mouse aspartate, and aspartate, respectively. Amino acids 1 and Hu homologs. The Hu proteins are an early marker of 5 are more variable—1 being leucine or phenylalanine neuronal development.10 Although not present in neu- and 5 being methionine or valine. The function of this roblasts, they first appear in early lineage neurons that 34-kd protein is unknown. Anti-Yo antibodies recog- are still capable of proliferation. They appear to be the nize epitopes present in this protein. earliest unequivocal marker of neuronal commitment in Two 62-kd proteins (CDR62-1 and CDR62-2) have CNS-stem cells. Hu-positive neurons that retain the ca- also been cloned and sequenced. These proteins have a pacity for proliferation can also be found in the lateral leucine zipper motif, which contains the epitope(s) rec- ventricle subependyma of adult rats10 and in the tempo- ognized by anti-Yo antibodies. The occurrence of leu- ral ventricular subependyma examined from autopsy of cine zipper motifs in the predicted open-reading frame epileptic patients. The role of the Hu proteins in the de- of these proteins suggests that they may play a role in velopment of neurons is indicated not only by their early the regulation of gene expression. Analysis of tumors from expression in neurons still capable of proliferation but patients with anti-Yo–associated PCD have demon- also by the fact that mutation of the Drosophila homolo- strated that the tumors express CDR34 and CDR62-1 but gous ELAV gene prevents development of the Drosophila not CDR62-2. Recently, Darnell and colleagues (oral com- nervous system. munication, 1999) have shown that the 62-kd protein HuD is expressed in a number of tumors, includ- binds to c-myc and have postulated that it exerts its ac- ing all small cell lung cancers and mostly all neuroblas- tivity by inhibiting the activity of the c-myc gene. The tomas, as well as occasional other tumors (including sev- role of the anti-Yo antibody in causing PCD is unclear, eral types of sarcoma and prostate carcinoma). but high titers of an antibody reacting predominantly with Whether, and if so how, the presence of antibodies Purkinje cells in a disease characterized by loss of all Pur- against Hu proteins in the serum samples of patients with kinje cells with relative sparing of the remainder of the paraneoplastic syndromes is associated with the destruc- CNS certainly suggests a role. T cells that specifically rec- tion of portions of the nervous system and with relative ognize Yo antigens have been found in the blood of PCD control of the growth of the underlying tumor is unclear. patients14 and appear to be cytotoxic for the tumor cells. What role the Hu proteins play in small cell lung cancer Whether this cytotoxic mechanism causes Purkinje cell and the other cancers in which they are expressed is also loss remains to be proven. unclear. The HuD protein in small cell lung cancers from patients with or without paraneoplastic syndromes is iden- OTHER PARANEOPLASTIC ANTIGENS tical to its neuronal counterpart and not mutated. Several other onconeural antigens have been identified by Yo PROTEINS examination of serum samples from patients with paraneoplastic syndromes. Antiamphiphysin antibodies are pre- The term Yo proteins refers to a family of proteins highly sent in serum samples of patients with stiff-man syndrome expressed in the cytoplasm of cerebellar Purkinje cells and and breast cancer or, less frequently, in patients with en- in the tumor cells (usually gynecologic or breast) of pa- cephalomyelitis associated with small cell lung cancer. Am- tients with anti-Yo–positive antibody paraneoplastic cer- phiphysin is a nerve terminal protein with a putative role ebellar degeneration (PCD). The anti-Yo antibody was first in endocytosis. The antiamphiphysin antibodies of these reported by Greenlee and Brashear11 in 1983, and later by patients predominantly react with the C-terminus of the Jaeckle et al12 in patients with ovarian cancer and sub- protein that contains an SH3 domain that interacts with acute cerebellar degeneration. In the rat or mouse brain, other proteins involved in synaptic vesicle endocytosis. anti-Yo serum at low dilution reacts with cerebellar Pur- The exact role of the antibodies in the pathogenesis of the kinje cells as well as some other large cells in the CNS and, stiff-man syndrome or encephalomyelitis is unknown. in at least 1 laboratory study, with Schwann cells. At higher A new family of paraneoplastic antigens (the Ma pro- dilutions, using human tissues, the reaction is restricted teins) has recently been identified. There are at least 5 to Purkinje cells of the cerebellum, to the tumors that are Ma proteins, the best characterized being Ma1 and Ma2. associated with anti-Yo–positive PCD, and about 30% of The expression of these proteins is highly restricted to ovarian cancers not associated with PCD. Surprisingly, neurons and spermatogenic cells of testis. In immuno- mRNA for Yo proteins is widely distributed not only in blots of neuronal proteins, the anti-Ma antibodies rec- the nervous system but throughout the body. The selec- ognize 2 bands of 37 and 40 kd that correspond to Ma1 tive expression of Yo proteins by Purkinje cells appears and Ma2. These antibodies are contained in the serum to be posttranscriptionally regulated. and spinal fluid of patients with paraneoplastic brain- The anti-Yo serum identifies 2 bands in immunob- stem and cerebellar dysfunction and are associated with lots of protein extracts of Purkinje cells. The bands had several types of tumors (lung, breast, parotid gland, col- relative molecular weights of 62 and 34 kd. Subse- on).15 The anti-Ta antibodies are present in the serum quently, an intermediate band of about 52 kd has also and spinal fluid of patients with paraneoplastic limbic and been discovered. brainstem encephalitis associated with testicular can- There are 3 types of Yo proteins: CDR34, CDR62-1, cer. These antibodies recognize epitopes mainly con- and CDR62-2. The first, cloned and sequenced by Drop- tained in Ma2 (40-kd neuronal protein).15 Some of these

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©1999 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 patients also develop mild cerebellar dysfunction. The stricted to the nervous system and having functions that Ma proteins are expressed by the tumors of patients with appear to be essential for the development and mainte- paraneoplastic syndromes but not by similar tumors from nance of neuronal function. These antibodies can be used patients without paraneoplastic syndromes. as probes to immunohistochemically localize the anti- PatientswiththeLambert-Eatonmyasthenicsyndrome gen in the nervous system, as well as probes to clone from develop antibodies that react with the active zones of the complementary DNA expression libraries genes that code presynaptic cholinergic synapses, blocking the entry of cal- for onconeural antigens. In each instance in which this cium necessary for the release of acetylcholine. The epi- has been done, the antigens have become of extraordi- topes recognized by their antibodies are contained in the nary interest in terms of nervous system function. P/Q-type voltage-gated calcium channels (VGCC) of the presynaptic cholinergic synapse. Similar channels are ex- Accepted for publication December 22, 1998. pressed in cerebellum and extracts of cerebellum labeled Supported in part by National Institutes of Health, with iodine 125-␻-conotoxin MVIIC (toxin that specifi- Bethesda, Md, grant NS26064 (Drs Dalmau and Posner). cally binds to the P/Q-type VGCC) are used in an immu- Dr Posner is the Evelyn Frew American Cancer Society Clini- noprecipitation assay to detect antibodies in patients with cal Research Professor. Lambert-Eaton myasthenic syndrome.16 Antibodies against Correspondingauthor: JeromeB.Posner,MD,1275York the ␤-subunit of the neuronal calcium channel and against Ave, New York, NY 10021 (e-mail: [email protected]). synaptotagmin have also been identified in the serum of patients with Lambert-Eaton myasthenic syndrome. Overall, these studies suggest that patients with Lam- REFERENCES bert-Eaton myasthenic syndrome develop antibodies di- 1. Dalmau JO, Posner JB. Neurological paraneoplastic syndromes. Neuroscien- rected against multiple epitopes, probably contained in tist. 1998;4:443-453. more than 1 subunit of the P/Q-type VGCC. It is un- 2. Graus F, Dalmau JO, Rene R, et al. Anti-Hu antibodies in patients with small-cell known whether all these antibodies are pathogenic or most lung cancer: association with complete response to therapy and improved sur- vival. J Clin Oncol. 1997;15:2866-2872. of them represent elements of a repertoire of immune re- 3. 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