Yo Antibodies Research Articles

A cerebellar degeneration-related protein 2-like cell-based assay for anti-Yo detection in patients with paraneoplastic cerebellar degeneration.

Commercially available tests for Yo antibody detection have low specificity for paraneoplastic cerebellar degeneration (PCD) because these assays use cerebellar degeneration-related protein 2 (CDR2) as the antigen, not CDR2-like (CDR2L). We aimed to test the hypothesis that use of a CDR2L cell-based assay (CBA), as an additional screening technique, would increase the accuracy of Yo-PCD diagnosis. An in-house CBA to test for anti-CDR2L antibodies was developed and used to screen sera from 48 patients with confirmed anti-Yo-associated PCD. Fifteen non-Yo PCD patients, 22 patients with ovarian cancer without neurological syndromes, 50 healthy blood donors, 10 multiple sclerosis, 15 Parkinson's disease, and five non-paraneoplastic ataxic patients were included as controls. Sera were also tested by western blot analysis using recombinant CDR2 and CDR2L proteins developed in house, by the commercially available line immunoassays from Ravo Diagnostika and Euroimmun, and by the CDR2 CBA from Euroimmun. The CDR2L CBA identified all 48 patients with Yo-PCD. No CDR2L CBA reaction was observed in any of the control sera. The western blot technique had lower sensitivity and specificity as sera from eight and six of the 48 Yo-PCD patients did not react with recombinant CDR2 or CDR2L, respectively. The CDR2L CBA is highly reliable for identification of Yo-PCD. Although our findings indicate that, currently, the combination of CDR2 and CDR2L yields the most reliable test results, it remains to be evaluated if a test for single anti-CDR2L positivity will serve as a sufficient biomarker for Yo-PCD diagnosis.

A rare case of paraneoplastic cerebellar ataxia secondary to Gynaecological malignancy

We report on a rare case of paraneoplastic syndrome (PS) that was discovered on completion of diagnostic work up to be a fallopian tube carcinoma. A 65year old female, presented with 1 month history of imbalance, gait instability, incoordination of right upper limb, vertigo and vomiting. Cerebrovascular accident and drug intoxication was excluded. Indicative of further diagnosis of paraneoplastic syndrome was presence of adnexal mass in pelvis with identification of onconeural anti-Yo antibodies, detection of which leads to the confirmation of diagnosis. The anti- Yo (Anti-Purkinje cell) antibodies that specifically damage Purkinje cells of the cerebellum. Anti- Yo related paraneoplastic cerebellar degeneration is most commonly found in women with gynecological and breast cancers.

BREAST CANCER ASSOCIATED ANTI YO-ANTIBODY MEDIATED PARANEOPLASTIC CEREBELLAR DEGENERATION: CASE SERIES AND REVIEW OF LITERATURE

Paraneoplastic cerebellar degeneration (PCD) is a rare immune mediated disorder characterized by progressive cerebellar ataxia in presence of onconeural antibodies which occurs due to an indirect effect of underlying malignancy i.e. small cell lung cancer (SCLC), breast and gynecologic cancer, and Hodgkin lymphoma. In about 50% of patients neurological manifestation of Paraneoplastic cerebellar degeneration occurs prior to detection of carcinoma. Anti-Yo Antibody is the commonest antibody present in patients with Paraneoplastic cerebellar degeneration which is associated with breast carcinoma. We describe 3 female patients with anti YO antibody mediated PCD with breast cancer. One patient had a previous diagnosis of breast cancer with post mastectomy status one year back. Two of them presented with ataxia and on further examination, breast lump was found. All three patients had symmetrical ataxia with one patient had severely debilitating ataxia and was not able to walk unassisted. Magnetic resonance imaging brain showed cerebellar atrophy in two patients while one patient had normal MRI. Anti- YO antibody was strongly positive in all the three patients. All patients were given immunotherapy (corticosteroids in 2, Intravenous immunoglobulin in 1) with 1 patient showed modest improvement These case highlights the need to consider for workup for paraneoplastic cerebellar degeneration in female patients presenting with subacute to chronic progressive ataxia, so that the tumors can be detected and treated in early stage with a good outcome.

Paraneoplastic cerebellar degeneration: A rare paraneoplastic syndrome

Paraneoplastic syndrome are rare disorders associated with cancers. Among then paraneoplastic cerebellar degeneration is classical PCS, presents acutely and sub acutely with walking incoordination, slurring of voice. Anti YO anti bodies are strongly associated with this PCS. Presence of anti YO antibody shows poor prognosis, and mild recovery with immunosuppressants. Treatment is not very promising in severely affected patient.

Internal audit of two antineuronal immunoblots and the role of indirect immunofluorescence in sample screening

Anti-neuronal antibodies are associated with a range of clinical phenotypes that are often preceded by malignancy. Most of these antibodies can be identified by indirect immunofluorescence (IIF) using commercial primate neural tissue slides. The EUROImmun 12 and upgraded RAVO 14 antigen line immunoblots were directly compared to replace a 9 antigen RAVO immunoblot. Initial assessment was with samples with known positive specificities by IIF. The second phase involved parallel testing of routine pooled negative IIF samples as per institutional standard antineuronal testing algorithm. IIF results and clinical correlation were used to arbitrate on discordant immunoblot results. Correlation in known positives was 80%. The EUROImmun immunoblot did not identify disease causing SOX1 and Recoverin antibodies. Routine pooled analysis did not identify discrepancy between the platforms. Assessment of 318 patient samples did not reveal any cases where a diagnosis was correctly identified by line immunoblot and not IIF. A single sample with positive Yo antibodies was identified by both platforms without clinical or IIF correlation, making this a likely false positive. Subsequent to this audit, Westmead ICPMR has migrated to the 14 antigen RAVO line blot for confirmation of positive IIF or for patients with equivocal results only.

Paraneoplastic Cerebellar Degeneration: The Importance of Including CDR2L as a Diagnostic Marker.

ObjectiveInvestigate the value of including cerebellar degeneration-related protein 2-like (CDR2L) as a marker in commercial diagnostic tests for anti-Yo–associated paraneoplastic cerebellar degeneration (PCD).MethodsWe included sera and CSF samples from 24 patients with suspected PCD (6 of whom had PCD with underlying gynecologic or breast cancer), who were positive for Yo antibodies using the commercially available, paraneoplastic neurologic syndromes (PNS) 14 Line Assay from Ravo Diagnostika. The samples were further evaluated using the EUROLINE PNS 12 Ag Line Assay and a cell-based assay (CBA) from Euroimmun. For confirmation of positive lineblot results, we used indirect immunofluorescence of rat cerebellar sections. We also tested all samples in 2 assays developed in-house: a CBA for CDR2L and a Western blot analysis using recombinant cerebellar degeneration-related protein 2 (CDR2) and CDR2L proteins.ResultsIn PNS 14 and PNS 12 Ag Line Assays, anti-CDR2 reactivity was observed for 24 (100%) and 20 (83%) of the 24 samples, respectively. Thirteen of 24 subjects (54%) were also positive using the Euroimmun CBA. Rat cerebellar immunofluorescence was the best confirmatory test. In our in-house CBA for CDR2L and Western blot for CDR2 and CDR2L, only the 6 patients with confirmed PCD reacted with CDR2L.ConclusionsCommercially available tests for Yo antibody detection have low specificity for PCD because these assays use CDR2 as antigen. By adding a test for CDR2L, which is the major Yo antigen, the accuracy of PCD diagnosis greatly improved.Classification of EvidenceThis study provides Class III evidence that a CBA for CDR2L accurately identifies patients with PCD.

Localization of CDR2L and CDR2 in paraneoplastic cerebellar degeneration.

ObjectiveIdentify the subcellular location and potential binding partners of two cerebellar degeneration‐related proteins, CDR2L and CDR2, associated with anti‐Yo‐mediated paraneoplastic cerebellar degeneration.MethodsCancer cells, rat Purkinje neuron cultures, and human cerebellar sections were exposed to cerebrospinal fluid and serum from patients with paraneoplastic cerebellar degeneration with Yo antibodies and with several antibodies against CDR2L and CDR2. We used mass spectrometry‐based proteomics, super‐resolution microscopy, proximity ligation assay, and co‐immunoprecipitation to verify the antibodies and to identify potential binding partners.ResultsWe confirmed the CDR2L specificity of Yo antibodies by mass spectrometry‐based proteomics and found that CDR2L localized to the cytoplasm and CDR2 to the nucleus. CDR2L co‐localized with the 40S ribosomal protein S6, while CDR2 co‐localized with the nuclear speckle proteins SON, eukaryotic initiation factor 4A‐III, and serine/arginine‐rich splicing factor 2.InterpretationWe showed that Yo antibodies specifically bind to CDR2L in Purkinje neurons of PCD patients where they potentially interfere with the function of the ribosomal machinery resulting in disrupted mRNA translation and/or protein synthesis. Our findings demonstrating that CDR2L interacts with ribosomal proteins and CDR2 with nuclear speckle proteins is an important step toward understanding PCD pathogenesis.

The Diagnostic Value of Onconeural Antibodies Depends on How They Are Tested

Detection of onconeural antibodies is important because establishes a definitive diagnosis of paraneoplastic neurological syndrome (PNS). The recommended method for diagnosis of onconeural antibodies is by immunohistochemistry on rodent brain sections and confirmation of results by immunoblot. However, in many diagnostic laboratories samples are only tested with commercial line blots. In this study we inquired whether this change in diagnostic methodology (line blot alone vs. combined immunohistochemistry and line blot) would affect the results. Among 439 samples examined by immunohistochemistry and a commercial line blot (Euroimmun, Lübeck, Germany) 96 (22%) were positive by line blot, and their clinical information was reviewed. Onconeural antibodies were detected by both assays in 46/96 (48%) patients (concordant group) whereas 50 (52%) were only positive by line blot (discordant group). In the concordant group 42/46 (91%) patients had a definite diagnosis of PNS whereas in the discordant group only 4/50 (8%) had PNS (p < 0.00001). None of the 14 patients with ZIC4 antibodies and 1/13 (8%) with Yo antibodies demonstrated only by line blot had PNS. These findings show a robust diagnostic value of combined diagnostic techniques, and both should be used to demonstrate onconeural antibodies, If antibody testing is performed only with line blot assay, positive bands should be confirmed by rodent brain immunohistochemistry. For ZIC4 or Yo antibody testing, line blot positivity with negative immunohistochemistry has no diagnostic significance, and for the rest of onconeural antibodies the predictive diagnostic value is low.

Paraneoplastic ataxic syndrome with anti-Yo antibodies in breast and ovarian cancer: A retrospective analysis.

e18089 Background: Paraneoplastic cerebellar syndrome is a rare immunological reaction caused most commonly by Anti-Yo or Purkinje cell cytoplasmic antibody type 1(PCA1) to cerebellar degeneration protein 2(CDR2), found in the cerebellum and ectopically produced by tumor. Most cases are reported in women with HER2+ breast and ovarian cancers with underlying breast cancer patients having relatively better prognosis. Treatment initiation within one month of symptom onset has shown better outcomes. Methods: A retrospective analysis was conducted using a clinical database at a single institution and included 3 patients with a cancer diagnosis and ataxic symptoms diagnosed between 2016 and 2020. Data collection included age, gender, performance status, site of disease, pathology, diagnostic work up, treatment and overall survival (OS). Results: The study included 3 patients who presented with new onset ataxic symptoms with the median time of cancer diagnosis from onset of symptoms being 5 months (range 4-7). Median age was 62 years (range 59-83), all 3 patients were females and functionally independent before symptom onset. Out of 3 patients 2 had HER2+ breast cancer (one with IHC 3+ and one with equivocal IHC but 20 HER2 signals/nucleus) and the third had ovarian carcinoma. All 3 patients had stage IIIA disease as per AJCC 8th edition and presented with bilateral extremity weakness, ataxia, visual disturbances, vertigo and nausea/vomiting. Extensive neurological work up including MRI brain, CSF analysis, EEG were inconclusive except for high titres of anti- Yo antibodies in all patients. All patients were treated with cancer directed therapy and immunomodulation with plasma exchange, IVIG and steroids. The median OS being 22 months (range 12-28) with 2 patients with underlying breast cancer alive at the time of the analysis albeit there has been no neurological recovery, despite IVIG, steroids, and plasma exchange. Conclusions: The anti-Yo associated paraneoplastic ataxic syndrome most commonly associated with breast and pelvic tumors in women has a very poor prognosis despite anti-tumor and immunomodulating therapies, leaving most patients bed-ridden. The neurologic damage is irreparably incurred once the antibodies attack cerebellar cells. Thus, it is critical for clinicians to recognize the potential signs and symptoms as early as possible, so that treatment can be started, and long term symptoms are minimized. Further studies are needed to know the exact mechanism of this syndrome and provide evidence based treatment options.

CDR2L Is the Major Yo Antibody Target in Paraneoplastic Cerebellar Degeneration.

The pathogenesis of Yo-mediated paraneoplastic cerebellar degeneration (PCD) is unclear. We applied cerebrospinal fluid and serum from PCD patients as well as CDR2 and CDR2L antibodies to neuronal tissue, cancer cell lines, and cells transfected with recombinant CDR2 and CDR2L to elucidate which is the major antigen of Yo antibodies. We found that Yo antibodies bound endogenous CDR2L, but not endogenous CDR2. However, Yo antibodies can bind the recombinant CDR2 protein used in routine clinical testing for these antibodies. Because Yo antibodies only bind endogenous CDR2L, we conclude that CDR2L is the major antigen of Yo antibodies in PCD. ANN NEUROL 2019;86:316-321.

Paraneoplastic cerebellar degeneration: Yo antibody alters mitochondrial calcium buffering capacity

AimNeurodegeneration is associated with dysfunction of calcium buffering capacity and thereby sustained cellular and mitochondrial calcium overload. Paraneoplastic cerebellar degeneration (PCD), characterized by progressive Purkinje neurone degeneration following paraneoplastic Yo antibody internalization and binding to cerebellar degeneration‐related protein CDR2 and CDR2L, has been linked to intracellular calcium homeostasis imbalance due to calbindin D28k malfunction. Therefore, we hypothesized that Yo antibody internalization affects not only calbindin calcium binding capacity, but also calcium‐sensitive mitochondrial‐associated signalling, causing mitochondrial calcium overload and thereby Purkinje neurone death.MethodsImmunohistochemically, we evaluated cerebellar organotypic slice cultures of rat brains after inducing PCD through the application of Yo antibody‐positive PCD patient sera or purified antibodies against CDR2 and CDR2L how pharmacologically biased mitochondrial signalling affected PCD pathology.ResultsWe found that Yo antibody internalization into Purkinje neurons caused depletion of Purkinje neurone calbindin‐immunoreactivity, cannabinoid 1 receptor over‐activation and alterations in the actions of the mitochondria permeability transition pore (MPTP), voltage‐dependent anion channels, reactive oxygen species (ROS) and Na+/Ca2+ exchangers (NCX). The pathological mechanisms caused by Yo antibody binding to CDR2 or CDR2L differed between the two targets. Yo‐CDR2 binding did not alter the mitochondrial calcium retention capacity, cyclophilin D‐independent opening of MPTP or activity of NCX.ConclusionThese findings suggest that minimizing intracellular calcium overload toxicity either directly with cyclosporin‐A or indirectly with cannabidiol or the ROS scavenger butylated hydroxytoluene promotes mitochondrial calcium homeostasis and may therefore be used as future neuroprotective therapy for PCD patients.

Cerebellar degeneration-related proteins 2 and 2-like are present in ovarian cancer in patients with and without Yo antibodies.

Cerebellar degeneration-related protein 2 (CDR2) has been presumed to be the main antigen for the onconeural antibody Yo, which is strongly associated with ovarian cancer and paraneoplastic cerebellar degeneration (PCD). Recent data show that Yo antibodies also target the CDR2-like protein (CDR2L). We, therefore, examined the expression of CDR2 and CDR2L in ovarian cancer tissue from patients with and without Yo antibodies and from various other cancerous and normal human tissues. Ovarian cancer tissue and serum samples from 16 patients were included in the study (four with anti-Yo and PCD, two with anti-Yo without PCD, five with only CDR2L antibodies, and five without onconeural antibodies). Clinical data were available for all patients. The human tissues were examined by western blot and immunohistochemistry using rabbit CDR2 and CDR2L antibodies. Ovarian cancers from all 16 patients expressed CDR2 and CDR2L proteins. Both proteins were also present in normal and cancer tissue from mammary tissue, kidney, ovary, prostate, and testis. CDR2L is present in ovarian cancers from patients with and without Yo antibodies as was shown previously for CDR2. In addition, both CDR2 and CDR2L proteins are more widely expressed than previously thought, both in normal and cancerous tissues.

Coexisting neuronal autoantibodies among children with demyelinating syndromes

ObjectivesTo determine the incidence and clinical relevance of neuronal autoantibodies in children with demyelinating syndromes. MethodsWe conducted a prospective study including 31 consecutive children with demyelinating syndromes. Four patients with N-Methyl-D-aspartate receptor (NMDAR) encephalitis, 32 patients with Guillain-Barre syndrome, 13 children with benign childhood epilepsy, and 28 healthy children were used as controls. Prior to initiating immunomodulatory therapy, serum samples were tested for antibodies against NMDAR, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) 1, AMPAR2, leucine-rich glioma-activated protein 1, contactin-associated protein 2, gamma-aminobutyric acid B receptors, paraneoplastic ma antigen 2 (PNMA2/Ta), Yo, Ri, Hu, CV2, amphiphysin, and aquaporin-4 by indirect immunofluorescence assays. ResultsThree anti-neuronal antibodies were detected; NMDAR antibody in one with multiple sclerosis, PNMA2/Ta antibody in one with multiple sclerosis, and Yo antibody in one with clinically isolated syndrome. The positivity rate of neuronal autoantibodies in demyelinating syndrome was 10%. All seropositive patients were found to be negative for tumor screening. None of these patients exhibited symptoms of encephalitis. ConclusionChildren with demyelinating syndromes without symptoms of encephalitis can be positive for anti-neuronal antibodies.

Autoantibody diversity in paraneoplastic syndromes and related disorders: The need for a more guided screening approach

BackgroundSignificant progress has been made in understanding the role and diversity of autoantibodies in the pathogenesis, diagnosis and management of paraneoplastic syndrome (PNS) and related autoimmune neurologic diseases. We evaluated the positivity rates for diverse autoantibody panels to rationalize testing strategies and utilization. MethodsThe result patterns for different autoantibody panels for PNS offered at 2 reference laboratories in the U.S. were retrospectively reviewed for the same period. The positivity rates were evaluated and compared for specific autoantibodies within panels offered at both laboratories. ResultsFor the Hu, Ri, Yo, and amphiphysin antibodies offered by both laboratories, no significant difference in positivity rates was observed. The positivity rates for non-classic PNS markers were 0% [AGNA and PCCA-Tr], and 0.06% [ANNA-3 and PCAC-2] while the prevalence of antibodies associated with neuromuscular autoimmunity varied from 1.40% to 4.44% [Striated muscle, AChR binding, ganglionic AChR, VGCC, P/Q- and N-type VGCC]. ConclusionsThe data suggest that test utilization could be substantially improved based on ordering practice geared towards clinical manifestations and prevalence of autoantibodies. Concerted efforts towards streamlining diagnostic algorithms based on risk, clinical manifestations, characterization of autoantibodies and their associations as well as therapeutic strategies are needed.

Paraneoplastic syndrome-associated neuronal antibodies in adult ADHD

A high seroprevalence of Yo antibodies targeting cerebellar Purkinje cells was recently reported in children with attention deficit/hyperactivity disorder (ADHD). We investigated the presence of 8 paraneoplastic neurological syndrome (PNS)-associated antibodies including anti-Yo in 169 adult ADHD patients. No associations between ADHD and serum Yo antibodies or other antibodies associated with PNS were found. However, 10 out of 48 ADHD patient sera analyzed by immunofluorescence presented antibodies targeting cerebellar Purkinje cells. This reactivity probably represents the presence of low levels of antibodies against multiple cellular hitherto unknown antigens with little to no clinical significance.

Paraneoplastic CDR2 and CDR2L antibodies affect Purkinje cell calcium homeostasis.

Paraneoplastic cerebellar degeneration (PCD) is characterized by loss of Purkinje cells (PCs) associated with progressive pancerebellar dysfunction in the presence of onconeural Yo antibodies. These antibodies recognize the cerebellar degeneration-related antigens CDR2 and CDR2L. Response to PCD therapy is disappointing due to limited understanding of the neuropathological mechanisms. Here, we report the pathological role of CDR antibodies on the calcium homeostasis in PCs. We developed an antibody-mediated PCD model based on co-incubation of cerebellar organotypic slice culture with human patient serum or rabbit CDR2 and CDR2L antibodies. The CDR antibody-induced pathology was investigated by high-resolution multiphoton imaging and biochemical analysis. Both human and rabbit CDR antibodies were rapidly internalized by PCs and led to reduced immunoreactivity of calbindin D28K (CB) and L7/Pcp-2 as well as reduced dendritic arborizations in the remaining PCs. Washout of the CDR antibodies partially recovered CB immunoreactivity, suggesting a transient structural change in CB calcium-binding site. We discovered that CDR2 and CB co-immunoprecipitate. Furthermore, the expression levels of voltage-gated calcium channel Cav2.1, protein kinase C gamma and calcium-dependent protease, calpain-2, were increased after CDR antibody internalization. Inhibition of these signaling pathways prevented or attenuated CDR antibody-induced CB and L7/Pcp-2 immunoreactivity loss, morphological changes and increased protein expression. These results signify that CDR antibody internalization causes dysregulation of cell calcium homeostasis. Hence, drugs that modulate these events may represent novel neuroprotective therapies that limit the damaging effects of CDR antibodies and prevent PC neurodegeneration.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-014-1351-6) contains supplementary material, which is available to authorized users.

Carbonic anhydrase‐related protein VIII antibodies and paraneoplastic cerebellar degeneration

Carbonic anhydrase‐related protein <scp>VIII</scp> antibodies and paraneoplastic cerebellar degeneration

CDR2L Antibodies: A New Player in Paraneoplastic Cerebellar Degeneration

ObjectiveYo antibodies are associated with paraneoplastic cerebellar degeneration (PCD). We have characterized Yo sera by measuring CDR2 and CDR2L antibodies and the localization of their antigens.MethodsForty-two Yo sera from patients with paraneoplastic neurological syndromes (PNS), 179 sera from ovarian and 114 sera from breast cancer patients without PNS and 100 blood donors were screened for CDR2 and CDR2L antibodies by radioactive immune assay (RIA). Fluorescence microscopy was also used to determine the presence of CDR2 or CDR2L antibodies by staining of HeLa cells transfected with CDR2 or CDR2L fused to green fluorescent protein (GFP). Confocal microscopy was further used to localize the CDR2 and CDR2L proteins.ResultsRIA showed that 36 of the 42 Yo positive sera contained CDR2 and CDR2L antibodies whereas 6 sera contained only CDR2 antibodies. Five of the ovarian cancer patients had CDR2L antibodies and 4 of the breast cancer patients had either CDR2 or CDR2L antibodies. Only patients with both antibodies had PCD. RIA and staining of transfected cells showed similar results. Yo antibodies were not present in the 100 blood donors. Confocal microscopy showed that CDR2 and CDR2L were localized to the cytoplasm, whereas CDR2L was also present on the cell membrane.InterpretationYo sera usually contain CDR2 and CDR2L antibodies and both antibodies are associated with PCD. Since only CDR2L is localized to the cell membrane it is likely that CDR2L antibodies may be of primary pathogenic importance for the development of PCD.

Avidity of onconeural antibodies is of clinical relevance.

Onconeural antibodies are important in the detection of paraneoplastic neurological syndromes (PNS). The avidity of Hu, Yo, and CRMP5 antibodies from 100 patients was determined by immunoprecipitation (IP), and 13 of the Yo positive sera were also tested by surface plasmon resonance (SPR). There was a significant association between the results from IP and SPR. Yo antibodies had higher avidity than Hu and CRMP5 antibodies, and both high- and low-avidity antibodies were associated with tumors and PNS. High-avidity Yo antibodies were mainly associated with ovarian cancer, whereas high-avidity Hu and CRMP5 antibodies were mainly associated with small-cell lung cancer. Low-avidity CRMP5 and Yo antibodies were less often detected by a commercial line blot than high-avidity antibodies. The failure to detect low-avidity onconeural antibodies may result in under diagnosis of PNS.

Human epidermal growth factor receptor 2 overexpression in breast cancer of patients with anti-Yo-associated paraneoplastic cerebellar degeneration

Isolated case reports suggest that breast tumors from patients with paraneoplastic cerebellar degeneration (PCD) and Yo antibodies overexpress human epidermal growth factor receptor 2 (HER2). HER2 overexpression is present in 15%-25% of breast cancers and is associated with poor prognosis. We retrospectively analyzed the status of HER2 in breast tumors of 27 patients with anti-Yo-associated PCD to evaluate whether HER2 overexpression in this group of patients is higher than expected. In addition, we analyzed HER2 status of 19 breast tumors from patients with paraneoplastic neurological syndromes and Ri antibodies to see whether HER2 was specifically related to anti-Yo-associated PCD. We also assessed cdr2 expression (the onconeural antigen recognized by Yo antibodies) in 21 HER2-positive breast tumors from patients without paraneoplastic neurological syndromes. HER2 was overexpressed in 26 patients (96.3%) with anti-Yo-associated PCD but only in 2 patients (10.5%) with paraneoplastic neurological syndromes associated with Ri antibodies (P< .0001). Only 5 (23.8%) of the 21 HER2-positive breast tumors showed cdr2 immunoreactivity. This study shows a very high frequency of HER2 overexpression in breast cancers in patients with anti-Yo-associated PCD but not in those from patients with Ri antibodies. Although the expression of cdr2 onconeural antigen is not high in HER2-positive breast cancers, HER2 overexpression seems to be an important requirement to develop an anti-Yo-associated PCD.