Non-coding recurrent mutations in chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia (CLL) is a frequent disease in which the genetic alterations determining the clinicobiological behaviour are not fully understood. Here we describe a comprehensive evaluation of the genomic landscape of 452 CLL cases and 54 patients with monoclonal B-lymphocytosis, a precursor disorder. We extend the number of CLL driver alterations, including changes in ZNF292, ZMYM3, ARID1A and PTPN11. We also identify novel recurrent mutations in non-coding regions, including the 3' region of NOTCH1, which cause aberrant splicing events, increase NOTCH1 activity and result in a more aggressive disease. In addition, mutations in an enhancer located on chromosome 9p13 result in reduced expression of the B-cell-specific transcription factor PAX5. The accumulative number of driver alterations (0 to ≥4) discriminated between patients with differences in clinical behaviour. This study provides an integrated portrait of the CLL genomic landscape, identifies new recurrent driver mutations of the disease, and suggests clinical interventions that may improve the management of this neoplasia.

Olfactory mucosa stem cells: An available candidate for the treatment of the Parkinson's disease.

Olfactory ectomesenchymal stem cells (OE-MSCs) possess the immunosuppressive activity and regeneration capacity and hold a lot of promises for neurodegenerative disorders treatment. This study aimed to determine OE-MSCs which are able to augment and differentiate into functional neurons and regenerate the CNS and also examine whether the implantation of OE-MSCs in the pars compacta of the substantia nigra (SNpc) can improve Parkinson's symptoms in a rat model-induced with 6-hydroxydopamine. We isolated OE-MSCs from lamina propria in olfactory mucosa and characterized them using flow cytometry and immunocytochemistry. The therapeutic potential of OE-MSCs was evaluated by the transplantation of isolated cells using a rat model of acute SN injury as a Parkinson's disease. Significant behavioral improvement in Parkinsonian rats was elicited by the OE-MSCs. The results demonstrate that the expression of PAX2, PAX5, PITX3, dopamine transporter, and tyrosine hydroxylase was increased by OE-MSCs compared to the control group which is analyzed with real-time polymerase chain reaction technique and immunohistochemical staining. In the outcome, the transplantation of 1,1'-dioctadecyl-3,3,3'3'-tetramethyl indocarbocyanine perchlorate labeled OE-MSCs that were fully differentiated to dopaminergic neurons contribute to a substantial improvement in patients with Parkinson's. Together, our results provide that using OE-MSCs in neurodegenerative disorders might lead to better neural regeneration.

Tumor CD73/A2aR adenosine immunosuppressive axis and tumor-infiltrating lymphocytes in diffuse large B-cell lymphoma: correlations with clinicopathological characteristics and clinical outcome.

Novel immune checkpoint blockades, including those targeting CD73 and A2aR, are being evaluated in malignancies in clinical trials. Here, we investigated the expression of CD73 and A2aR as well as tumor-infiltrating lymphocytes (TILs), and analyzed their correlations with clinicopathological characteristics and survival in diffuse large B-cell lymphoma (DLBCL). We found that CD73 expression on tumor cells, rather than the total protein and gene levels of CD73, was associated with survival. Patients with CD73+ /Pax-5+ (median survival, 57.8 months; 95% CI, 46.4-69.3) experienced significantly poorer outcomes than those with CD73- /Pax-5+ (median survival, 73.5 months; 95% CI, 65.9-81.2). Additionally, A2aR expression on both total TILs and CD8+ TILs was correlated with survival. Patients with A2aR+ TILs (median survival, 53.3 months; 95% CI, 40.6-66.0) had a significantly shorter survival time than patients with A2aR- TILs (median survival, 74.5 months; 95% CI, 67.5-81.5). Spearman's rank test showed that CD73 expression on tumor cells was positively correlated with A2aR expression on TILs (R = 0.395, p = 0.001). We further found that patients could be more precisely stratified through the combination of CD73 tumor cell expression and A2aR TILs expression, and patients with CD73+ /Pax-5+ and A2aR+ TILs experienced the worst outcome. We also revealed that patients with CD73+ /Pax-5+ and low CD8+ TILs or low absolute lymphocyte counts had unfavorable outcomes. Overall, our findings uncovered that patients with CD73+ on tumor cells as well as A2aR+ on TILs or low CD8+ TILs exhibited inferior survival, supporting potential combination strategies using CD73/A2aR immunosuppressive blockades as treatment options for DLBCL patients.

The expression of terminal deoxynucleotidyl transferase and paired box gene 5 in Merkel cell carcinomas and its relation to the presence of Merkel cell polyomavirus DNA.

BACKGROUND: Merkel cell carcinoma (MCC) tumor samples frequently express B-lymphoid lineage markers. However, the reasons for expression of specific B-lymphoid lineage markers are still unclear. We studied the expression of TdT and PAX5 (two B-cell lymphoid lineage markers) in a large pool of MCC tissue microarray samples. METHODS: Immunoexpression and staining intensities of TdT and Pax-5 were statistically correlated with patient, tumor, Merkel cell polyomavirus (MCV), and disease-specific parameters. RESULTS: In a cohort of 117 MCC patients and their corresponding tumor samples, TdT was expressed in 37 (31.6%) samples and PAX5 in 26 (22.2%). Simultaneous immunostaining for TdT and PAX5 was observed in 13 (11.1%) samples. A statistically significant relationship was observed between MCV virus copy number and positive TdT expression (P = 0.0056). Similarly, a significant relationship was also observed between positive TdT and tumor MCV virus positivity (P = 0.000495). CONCLUSION: We observed frequent TdT and PAX5 immunoexpression in MCC tumor samples. However, simultaneous immunoexpression of these markers was scarce. TdT expression was statistically significantly associated with MCV positivity. The absence of a statistically significant association between tumor parameters and disease progression markers undermines the systemic use of these markers in clinical practice.

Molecular characterization of acute lymphoblastic leukemia with high CRLF2 gene expression in childhood.

BACKGROUND: A high-level expression of the CRLF2 gene is frequent in precursor B-cell acute lymphoblastic leukemia (pB-ALL) and can be caused by different genetic aberrations. The presence of the most frequent alteration, the P2RY8/CRLF2 fusion, was shown to be associated with a high relapse incidence in children treated according to ALL-Berlin-Frankfurt-Münster (BFM) protocols, which is poorly understood. Moreover, the frequency of other alterations has not been systematically analyzed yet. PROCEDURE: CRLF2 mRNA expression and potential genetic aberrations causing a CRLF2 high expression were prospectively assessed in 1,105 patients treated according to the Associazione Italiana Ematologia Oncologia Pediatrica (AIEOP)-BFM ALL 2009 protocol. Additionally, we determined copy number alterations in selected B-cell differentiation genes for all CRLF2 high-expressing pB-ALL cases, as well as JAK2 and CRLF2 mutations. RESULTS: A CRLF2 high expression was detected in 26/178 (15%) T-cell acute lymphoblastic leukemia (T-ALL) cases, 21 of them (81%) had been stratified as high-risk patients by treatment response. In pB-ALL, a CRLF2 high expression was determined in 91/927 (10%) cases; the P2RY8/CRLF2 rearrangement in 44/91 (48%) of them, supernumerary copies of CRLF2 in 18/91 (20%), and, notably, the IGH/CRLF2 translocation was detected in 16/91 (18%). Remarkably, 7 of 16 (44%) patients with IGH/CRLF2 translocation had already relapsed. P2RY8/CRLF2- and IGH/CRLF2-positive samples (70 and 94%, respectively) were characterized by a high frequency of additional deletions in B-cell differentiation genes such as IKZF1 or PAX5. CONCLUSION: Our data suggest that this high frequency of genetic aberrations in the context of a high CRLF2 expression could contribute to the high risk of relapse in P2RY8/CRLF2- and IGH/CRLF2-positive ALL.

Transcriptional regulation of the proto-oncogene Zfp521 by SPI1 (PU.1) and HOXC13.

The mouse zinc-finger gene Zfp521 (also known as ecotropic viral insertion site 3; Evi3; and ZNF521 in humans) has been identified as a B-cell proto-oncogene, causing leukemia in mice following retroviral insertions in its promoter region that drive Zfp521 over-expression. Furthermore, ZNF521 is expressed in human hematopoietic cells, and translocations between ZNF521 and PAX5 are associated with pediatric acute lymphoblastic leukemia. However, the regulatory factors that control Zfp521 expression directly have not been characterized. Here we demonstrate that the transcription factors SPI1 (PU.1) and HOXC13 synergistically regulate Zfp521 expression, and identify the regions of the Zfp521 promoter required for this transcriptional activity. We also show that SPI1 and HOXC13 activate Zfp521 in a dose-dependent manner. Our data support a role for this regulatory mechanism in vivo, as transgenic mice over-expressing Hoxc13 in the fetal liver show a strong correlation between Hoxc13 expression levels and Zfp521 expression. Overall these experiments provide insights into the regulation of Zfp521 expression in a nononcogenic context. The identification of transcription factors capable of activating Zfp521 provides a foundation for further investigation of the regulatory mechanisms involved in ZFP521-driven cell differentiation processes and diseases linked to Zfp521 mis-expression.

Level of PAX5 in differential diagnosis of non-Hodgkin's lymphoma.

BACKGROUND & OBJECTIVES: The PAX5, a paired box transcription factor and B-cell activator protein (BSAP), activates B-cell commitment genes and represses non-B-cell lineage genes. About 14 transcript variants of PAX5 have been observed in human. Any alteration in its expression pattern leads to lymphogenesis or associated diseases and carcinogenesis in non-lymphoid tissues. Its mechanisms of function in pathophysiology of non-Hodgkin's lymphoma (NHL) are unclear. This study was intended to explore influence of PAX5 in cascade of NHL pathogenesis and diagnosis. METHODS: Samples of 65 patients were evaluated by immunohistochemical staining for cellular localization of PAX5, CD19, CD3, cABL, p53, Ras and Raf and by TUNEL assay, RNA-isolation and reverse transcriptase (RT)-PCR, w0 estern blot analysis, and lactate dehydrogenase (LDH) specific staining. RESULTS: B-cell type NHL patients were positive for PAX5, p53, Ras, CD19, Raf and CD3. All of them showed TUNEL-positive cells. The differential expression pattern of PAX5, CD19, p53, CD3, Zap700 , HIF 1α, Ras, Raf and MAPK (mitogen-activated protein kinase) at the levels of transcripts and proteins was observed. The LDH assay showed modulation of LDH4 and LDH5 isoforms in the lymph nodes of NHL patients. INTERPRETATION & CONCLUSIONS: The histological observations suggested that the patients represent diverse cases of NHL like mature B-cell type, mature T-cell type and high grade diffuse B-cell type NHL. The findings indicate that patients with NHL may also be analyzed for status of PAX5, CD19 and ZAP70, and their transcriptional and post-translational variants for the differential diagnosis of NHL and therapy.

Expression pattern of ISL-1, TTF-1 and PAX5 in olfactory neuroblastoma.

Olfactory neuroblastoma (ONB) is a rare neoplasm of the sinonasal area with neuroendocrine differentiation. ISL-1, TTF-1 and PAX5 are transcription factors that are frequently upregulated in tumors showing neuroendocrine differentiation. The aim of our study was to evaluate these markers in a group of ONBs. We included 11 ONBs from 4 large university hospitals. Immunohistochemical expression of TTF-1, PAX5 and ISL-1 was evaluated. TTF-1, ISL-1 and PAX5 were expressed in 3/11 cases (27.27%, h-score: 3-45), 7/11 cases (63.64%, h-score: 23-200), and in 3/11 cases (27.77%, h-score 3-85), respectively. The patient with the strongest PAX5 reactivity exhibited an aggressive clinical course with rapid dissemination to the spine and death shortly after the diagnosis. No significant correlation in the expression of PAX5 and TTF-1 ( = 0.43; p = 0.18) was observed. ISL-1 is widely expressed in tumors with neuroendocrine differentiation and therefore of limited value in their differential diagnosis. TTF-1 positivity does not exclude the diagnosis of primary ONB, although usually only a small percentage of cells are positive. PAX5 expression is infrequent (27.27%) in ONB; however, if present it can be associated with a very aggressive clinical course.

BRAD4 plays a critical role in germinal center response by regulating Bcl-6 and NF-κB activation.

Germinal center (GC) reaction is a T cell-dependent process in which activated B cells undergo clonal expansion and functional maturation to produce high affinity antibodies and differentiate into memory B cells(1). Here we demonstrate a new role of bromodomain and extraterminal domain (BET) protein BRD4 in GC B cell development. We found that during B cell differentiation stage there was an elevated expression of BRD4 in GC B cells and inhibition of BRD4 by small molecule inhibitors led to the suppression of GC formation and correspondent antibody responses in a Td antigen immunization model. At the molecular level, we found that the effects of BRD4 in primary GC B cell differentiation and B cell lymphoma were mediated through the impaired phosphorylation and translocation of NF-κBp65 and further down-regulation of B-cell lymphoma 6 (Bcl6) expression. Thus this study reveals a novel function of BRD4 in controlling the GC B cell development pathway.

Noncoordinate expression of J-chain and Blimp-1 define nurse shark plasma cell populations during ontogeny.

B-lymphocyte-induced maturation protein 1 (Blimp-1) is the master regulator of plasma cell development, controlling genes such as those encoding J-chain and secretory Ig heavy chain. However, some mammalian plasma cells do not express J-chain, and mammalian B1 cells secrete "natural" IgM antibodies without upregulating Blimp-1. While these results have been controversial in mammalian systems, here we describe subsets of normally occurring Blimp-1(-) antibody-secreting cells in nurse sharks, found in lymphoid tissues at all ontogenic stages. Sharks naturally produce large amounts of both pentameric (classically "19S") and monomeric (classically "7S") IgM, the latter an indicator of adaptive immunity. Consistent with the mammalian paradigm, shark Blimp-1 is expressed in splenic 7S IgM-secreting cells, though rarely detected in the J-chain(+) cells producing 19S IgM. Although IgM transcript levels are lower in J-chain(+) cells, these cells nevertheless secrete 19S IgM in the absence of Blimp-1, as demonstrated by ELISPOT and metabolic labeling. Additionally, cells in the shark BM equivalent (epigonal) are Blimp-1(-). Our data suggest that, in sharks, 19S-secreting cells and other secreting memory B cells in the epigonal are maintained for long periods without Blimp-1, but like in mammals, Blimp-1 is required for terminating the B-cell program following an adaptive immune response in the spleen.

PAX8 and PAX5 are differentially expressed in B-cell and T-cell lymphomas.

AIMS: The purpose of this study was to evaluate the expression patterns of B-cell specific activator protein (BSAP)/PAX5 and PAX8 in a wide variety of B-cell and T-cell neoplasms. METHODS AND RESULTS: A wide range of B-cell and T-cell neoplasms were subjected to immunohistochemical staining with antibodies against BSAP/PAX5 and PAX8 (polyclonal, pPAX8; monoclonal, mPAX8). Ten non-neoplastic lymph node specimens were examined with the same panel. All of the tested neoplastic and non-neoplastic B-cells reacted with the BSAP/PAX5 and pPAX8 antibodies, but did not show reactivity with the mPAX8 antibody. All tested T-cell neoplasms were negative using the BSAP/PAX5, pPAX8 and mPAX8 antibodies. CONCLUSIONS: This is the first study to show the absence of reactivity to an mPAX8 antibody in an expanded panel of B-cell lymphomas as well as in a variety of T-cell neoplasms. In contrast to the mPAX8 antibody, the pPAX8 antibody shows nuclear positivity in non-neoplastic B cells and mature B-cell neoplasms; however, this expression is probably a result of cross-reactivity with PAX5. Given that many laboratories use the pPAX8 antibody, a clear understanding of the differential staining patterns is necessary. The differential diagnosis of a B-cell lymphoma should be entertained when a pPAX8-positive, epithelial marker-negative neoplasm of uncertain primary origin is encountered.

Bone marrow B cell precursor number after allogeneic stem cell transplantation and GVHD development.

Patients without chronic graft-versus-host disease (cGVHD) have robust B cell reconstitution and are able to maintain B cell homeostasis after allogeneic hematopoietic stem cell transplantation (HSCT). To determine whether B lymphopoiesis differs before cGVHD develops, we examined bone marrow (BM) biopsies for terminal deoxynucleotidyl transferase (TdT) and PAX5 immunostaining early post-HSCT at day 30 when all patients have been shown to have high B cell activating factor (BAFF) levels. We found significantly greater numbers of BM B cell precursors in patients who did not develop cGVHD compared with those who developed cGVHD (median = 44 vs 2 cells/high powered field [hpf]; respectively; P < .001). Importantly, a significant increase in precursor B cells was maintained when patients receiving high-dose steroid therapy were excluded (median = 49 vs 20 cells/hpf; P = .017). Thus, we demonstrate the association of BM B cell production capacity in human GVHD development. Increased BM precursor B cell number may serve to predict good clinical outcome after HSCT.

Umbilical cord mesenchymal stem cells suppress B-cell proliferation and differentiation.

Mesenchymal stem cells (MSCs) may be obtained from umbilical cord as an abundant and noninvasive source. However, the immunomodulatory properties of umbilical cord-MSCs (UC-MSCs) were poorly studied. In this study, we aimed to investigate the effects of UC-MSCs on B-cell proliferation and differentiation. UC-MSCs were found to suppress the proliferation of B cells isolated from murine spleen. Moreover, UC-MSCs markedly suppressed B-cell differentiation as shown by the decreased number of CD138+cells and reduced levels of IgM and IgG production in coculture. As revealed by transwell experiments, soluble factors produced by UC-MSCs might be involved in mediating B-cell suppression. The Blimp-1 mRNA expression was suppressed whereas the PAX-5 mRNA expression was induced in coculture. Finally, UC-MSCs modified the phosphorylation pattern of Akt and p38 pathways, which were involved in B-cell proliferation and differentiation. These results may further support the potential therapeutic use of UC-MSCs in treating autoimmune disorders.

Single-cell analysis of the common lymphoid progenitor compartment reveals functional and molecular heterogeneity.

To investigate molecular events involved in the regulation of lymphoid lineage commitment, we crossed lambda5 reporter transgenic mice to Rag1-GFP knockin mice. This allowed us to subfractionate common lymphoid progenitors and pre-pro-B (fraction A) cells into lambda5(-)Rag1(low), lambda5(-)Rag1(high), and lambda5(+)Rag1(high) cells. Clonal in vitro differentiation analysis demonstrated that Rag1(low) cells gave rise to B/T and NK cells. Rag1(high) cells displayed reduced NK-cell potential with preserved capacity to generate B- and T-lineage cells, whereas the lambda5(+) cells were B-lineage restricted. Ebf1 and Pax5 expression was largely confined to the Rag1(high) populations. These cells also expressed a higher level of the surface protein LY6D, providing an additional tool for the analysis of early lymphoid development. These data suggest that the classic common lymphoid progenitor compartment composes a mixture of cells with relatively restricted lineage potentials, thus opening new possibilities to investigate early hematopoiesis.

Pax5 immunostaining in paraffin-embedded sections of canine non-Hodgkin lymphoma: a novel canine pan pre-B- and B-cell marker.

The Pax5 gene encodes the B-cell specific activator protein (BSAP), a member of the highly conserved paired box (PAX)-domain family of transcription factors and a key regulator in the development and differentiation of B-cells. Pax5 serves as a valuable B-cell marker in the classification of human lymphoma patients as it is restricted to lymphomas of B-cell lineage. In dogs, detection of Pax5 protein in lymphoma tissue has not been reported. Therefore, we have investigated the expression and detection of BSAP using a monoclonal anti-Pax5 antibody (anti-BSAP, clone 24) in canine lymphoma tissue samples to evaluate its diagnostic relevance as a B-cell marker. A series of 25 lymph nodes from 23 canine non-Hodgkin lymphoma patients, a reactive canine lymph node, and a normal non-reactive canine lymph node, were evaluated. All B-cell non-Hodgkin lymphomas (15) were found to express Pax5 protein. In addition, there was a strong correlation between Pax5 and CD79a expression. Three CD3 positive and five CD3 and CD79a positive lymphomas were immunophenotypically negative for anti-Pax5, indicating a T-cell lineage. In conclusion, anti-Pax5 antibody may offer an excellent B-cell marker in canine lymphomas.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated impairment of B cell differentiation involves dysregulation of paired box 5 (Pax5) isoform, Pax5a.

The persistent environmental contaminant and immunotoxicant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), markedly suppresses humoral immune responses. We recently reported impaired down-regulation of paired box 5 (Pax5), a repressor of B cell differentiation and concomitant suppression of the IgM response by TCDD in the murine CH12.LX B cell line. The objectives of the current study were to determine the impact of TCDD treatment on molecular outcomes characteristic of terminal B cell differentiation and to assess the role that Pax5 isoforms plays in the suppression of B cell differentiation by TCDD. In this study, we show that the highly abundant full-length Pax5 isoform, Pax5a, and at least two additional modestly expressed Pax5 isoforms were expressed in CH12.LX and splenic B cells. In lipopolysaccharide (LPS)-activated B cells, all of the identified Pax5 isoforms were synchronously down-regulated, and in the presence of TCDD cotreatment they were abnormally and synchronously elevated, suggesting a common mechanism of regulation. Furthermore, B cell differentiation markers X-box protein-1 and major histocompatibility complex class II showed that the levels to which Pax5 was derepressed by TCDD were sufficient to impair B cell differentiation and immunoglobulin gene expression. Confirming the involvement of Pax5, ectopic expression of Pax5a in the LPS-activated CH12.LX cells closely mimicked the suppression of the IgM response by TCDD. In summary, our results demonstrate that Pax5a has a critical role in both the TCDD-mediated impairment of B cell differentiation and the suppression of the humoral immune response.

Pax-5 protein expression in bladder cancer: a preliminary study that shows no correlation to grade, stage or clinical outcome.

AIMS: Pax (paired box) genes comprise a gene family crucial for cell differentiation that encodes a set of transcription factors. Recently, Pax-5 mRNA expression was suggested as a prognostic marker in bladder cancer (BC). However, a functional role of Pax-5 in BC is questionable because the protein expression was not determined in these studies. Therefore, we evaluated Pax-5 protein expression in an unselected, consecutive series of BC. METHODS: We immunohistochemically investigated Pax-5 protein expression in 100 archival bladder tumours and 22 normal urothelial samples using tissue microarray (TMA) technology and a monoclonal antibody against Pax-5. Staining intensity and percentage of positively stained cells were determined and correlated to histopathological characteristics of the tumours and clinical follow-up data. RESULTS: All 22 samples of histopathologically normal urothelium were negative for Pax-5 protein expression. Overall, 70 of 100 tumours gave interpretable results. Only seven of 70 (10%) cases showed a positive nuclear Pax-5 staining but without significant correlation to clinicopathological characteristics. Interestingly, we could observe Pax-5 positive lymphocytes located within the tumour or closely adjacent in the underlying stroma in 24 of 70 (34%) cases in our series. CONCLUSIONS: Pax-5 protein expression is infrequent in BC. Absence of correlation to clinicopathological characteristics suggests a minor functional role of Pax-5 in BC. Pax-5 positive lymphocytes within reactive infiltrates adjacent to the tumour warrant further studies evaluating biological, immunological and clinical relevance.

Paired Box 5 (PAX5) Expression in Poorly Differentiated Neuroendocrine Carcinoma of the Gastrointestinal and Pancreatobiliary Tract: Diagnostic and Potentially Therapeutic Implications.

Paired Box 5 (PAX5), a well-established B-cell marker, is preferentially expressed in small cell lung carcinoma and regulates the transcription of c-Met, offering a potential for therapeutic target. Its expression in poorly differentiated neuroendocrine carcinoma (PDNEC) of the digestive system has not been systemically evaluated. Archived pathology materials from 38 PDNEC in the gastrointestinal (GI) and pancreatobiliary (PB) tract were reviewed. Representative tumor sections were subject to immunohistochemical stain for PAX5, c-Met, and CD20. The extent of the staining [focal (<10%), patchy (10% to 50%), and diffuse (>50%)] and intensity (1+ to 3+) was evaluated. In total, 38 cases of well-differentiated neuroendocrine tumors from GI/PB tract served as controls. Nuclear PAX5 staining was observed in 16 (42%) cases in total, in 46% (11/24) of large cell neuroendocrine carcinoma, 67% (4/6) of small cell neuroendocrine carcinoma, and 13% (1/8) of mixed adenoneuroendocrine carcinoma, with diffuse (8), patchy (4), or focal (4) staining. The intensity was 3+ (2), 2+ (6), and 1+ (8). PAX5 expression was common in ampullary (4/5) and gastroesophageal junctional/esophageal (5/9) PDNEC. Two (5%) of 38 well-differentiated neuroendocrine tumors were positive for PAX5. Three PAX5 positive PDNEC showed weak cytoplasmic c-Met immunolabeling. CD20 was negative in all tumors. Our data show that PAX5 is commonly expressed in PDNEC of the GI/PB tract including small cell neuroendocrine carcinoma. This observation warrants a cautious approach when interpreting small biopsy of poorly differentiated neoplasms, especially when lymphoma is considered in the differentials. Further study of PAX5/c-Met signaling pathway and its potential therapeutic value in GI/PB PDNEC is warranted.

PAX-5 Positivity in Anaplastic Lymphoma Kinase-Negative Anaplastic Large Cell Lymphoma: A Case Report and Review of Literature.

Anaplastic lymphoma kinase (ALK)-negative anaplastic large cell lymphoma (ALCL) is a subtype of T-cell lymphomas that may mimic several other malignancies morphologically. With the help of immunohistochemistry, most cases of ALCL can be diagnosed on the basis of expression of T-cell lineage associated antigens. However, aberrations in the expression of immunohistochemical markers pose diagnostic challenges. The morphological and immunophenotypic features of ALCL show considerable overlap with classical Hodgkin lymphoma (CHL), which is a B-cell lymphoma. The 2008 World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues suggests that staining for the B-cell transcription factor, paired box 5 (PAX-5), is helpful in differentiating between them, as it is weakly positive in most CHL and should be negative in ALCL. We report a rare case of ALK-negative ALCL, which was positive for PAX-5 and CD15, mimicking CHL by immunohistochemistry, resulting in a diagnostic dilemma.