Pax-5 immunoexpression in various types of benign and malignant tumours: a high-throughput tissue microarray analysis

Homeobox Gene Expression Dysregulation as Potential Diagnostic and Prognostic Biomarkers in Bladder Cancer

Homeobox genes serve as master regulatory transcription factors that regulate gene expression during embryogenesis. A homeobox gene may have either tumor-promoting or tumor-suppressive properties depending on the specific organ or cell lineage where it is expressed. The dysregulation of homeobox genes has been reported in various human cancers, including bladder cancer. The dysregulated expression of homeobox genes has been associated with bladder cancer clinical outcomes. Although bladder cancer has high risk of tumor recurrence and progression, it is highly challenging for clinicians to accurately predict the risk of tumor recurrence and progression at the initial point of diagnosis. Cystoscopy is the routine surveillance method used to detect tumor recurrence. However, the procedure causes significant discomfort and pain that results in poor surveillance follow-up amongst patients. Therefore, the development of reliable non-invasive biomarkers for the early detection and monitoring of bladder cancer is crucial. This review provides a comprehensive overview of the diagnostic and prognostic potential of homeobox gene expression dysregulation in bladder cancer.

Immunohistochemical expression of transcription factors PAX5, OCT2, BCL6 and transcription regulator P53 in Non-Hodgkin lymphomas: A diagnostic cross-sectional study

Background

Non-Hodgkin lymphoma represents a heterogeneous group of tumors that constitute the seventh most common malignancy. Immunohistochemistry plays a major role in the detection of specific cell receptors. Transcription factors are a heterogeneous group of genes that play a critical role in the commitment, differentiation, and proliferation of specific cell types.

Methods

Paraffin-embedded tissue sections of non-Hodgkin lymphoma cases were selected, classified, and evaluated before staining with immunohistochemical markers (PAX5, OCT2, BCL6, and P53). Expression of the aforementioned markers was compared with histological subtypes and grades of lymphoma cases. Means of expression were also compared among histological subtypes.

Results

A total of 55 cases of NHL including 26 cases of low-grade lymphomas and 29 cases of high-grade lymphomas were included in the study. DLBCL and FL were the most common subtypes of high-grade and low-grade lymphomas respectively. Both PAX5 and OCT2 were positive in 44 cases of NHL (80%) including all cases of B-cell lymphomas. BCL6 and P53 demonstrated positive expression in 29.1% and 67.3% respectively. Interestingly, we found a significant association between the histological subtypes and the aforementioned markers (P-value<0.05).

Discussion

Expression of PAX5, OCT2, BCL, and P53 played a major role in the diagnosis and grading of non-Hodgkin lymphomas in our study. Both PAX5 and OCT2 provided more accuracy and specificity in the diagnosis of B-cell neoplasms compared to the classical B-cell markers. BCL6 expression reflected its role in germinal center formation in normal and malignant lymphoid tissues, and expression of P53 mirrored the accumulation of gene mutations in more aggressive lymphoma subtypes.

Conclusion

In this manuscript, we aimed to present a unique study that highlights the immunohistochemical expression of all the aforementioned factors among various histological subtypes of non-Hodgkin lymphomas with disparities in histological aggressiveness, highlighting a promising diagnostic and prognostic panel for non-Hodgkin lymphomas.

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Transcription factors are essential for the differentiation of B-cells.

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PAX5 and OCT2 provide more accuracy in the diagnosis of lymphomas.

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BCL6 expression reflects its role in germinal center formation.

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P53 expression is higher in aggressive subtypes.

Computing microRNA-gene interaction networks in pan-cancer using miRDriver

DNA copy number aberrated regions in cancer are known to harbor cancer driver genes and the short non-coding RNA molecules, i.e., microRNAs. In this study, we integrated the multi-omics datasets such as copy number aberration, DNA methylation, gene and microRNA expression to identify the signature microRNA-gene associations from frequently aberrated DNA regions across pan-cancer utilizing a LASSO-based regression approach. We studied 7294 patient samples associated with eighteen different cancer types from The Cancer Genome Atlas (TCGA) database and identified several cancer-specific and common microRNA-gene interactions enriched in experimentally validated microRNA-target interactions. We highlighted several oncogenic and tumor suppressor microRNAs that were cancer-specific and common in several cancer types. Our method substantially outperformed the five state-of-art methods in selecting significantly known microRNA-gene interactions in multiple cancer types. Several microRNAs and genes were found to be associated with tumor survival and progression. Selected target genes were found to be significantly enriched in cancer-related pathways, cancer hallmark and Gene Ontology (GO) terms. Furthermore, subtype-specific potential gene signatures were discovered in multiple cancer types.

Merkel Cell Polyomavirus: Oncogenesis in a Stable Genome

Merkel cell polyomavirus (MCV) is the causative agent for the majority of Merkel cell carcinoma (MCC) cases. Polyomavirus-associated MCC (MCCP) is characterized by the integration of MCV DNA into the tumor genome and a low tumor mutational burden. In contrast, nonviral MCC (MCCN) is characterized by a high tumor mutational burden induced by UV damage. Since the discovery of MCV, much work in the field has focused on understanding the molecular mechanisms of oncogenesis driven by the MCV tumor (T) antigens. Here, we review our current understanding of how the activities of large T (LT) and small T (ST) promote MCC oncogenesis in the absence of genomic instability. We highlight how both LT and ST inhibit tumor suppressors to evade growth suppression, an important cancer hallmark. We discuss ST interactions with cellular proteins, with an emphasis on those that contribute to sustaining proliferative signaling. Finally, we examine active areas of research into open questions in the field, including the origin of MCC and mechanisms of viral integration.

Feline and canine Merkel cell carcinoma: A case series and discussion on cellular origin

Merkel cell carcinoma (MCC) is in humans and cats a malignant cutaneous neuroendocrine carcinoma, whereas in dogs it possibly has a more benign behaviour. It may be cytologically confused with round cell tumours such as lymphoma because of its striking cytomorphologic similarity. Although MCC is considered to arise from Merkel cells, recent findings indicated that primitive (epi‐)dermal stem cells, early B‐cells or dermal fibroblasts were the origin of human MCC. The aim of our study was to evaluate a possible lymphoid origin in feline and canine MCCs. Specific analysis of CD3, PAX‐5, KIT and PARR assay were performed in 3 feline and 3 canine MCCs. All MCCs (6/6) were negative for CD3 and PAX‐5. KIT was expressed in all MCCs (6/6). Assessment of clonality by PARR assay exhibited a polyclonal B‐ and T‐cell receptor rearrangement in all five cases tested. In conclusion, a lymphoid origin of feline and canine MCCs could not be demonstrated. This is in contrast with human MCCs, that often express early B‐cell lineage markers.

Typical and Atypical Carcinoid Tumors of the Mediastinum: A Biomarker Analysis of 27 Cases With Clinical Correlation

Thymic typical and atypical carcinoids are rare and appear to be more aggressive than similar tumors in other sites. We retrospectively analyzed a group of biomarkers that hold therapeutic and prognostic utility, in 27 of these tumors. All cases were immunohistochemically stained with PAX5, MET, CRMP5, paxillin, p21, p27, EZH2, PDL-1, and Ki-67, and then H-scored. Clinicopathologic and survival data were statistically analyzed against staining (χ² test). Five- and 10-year-survival rates were 53% and 18%, respectively. Mitotic counts ≥4 per 2 mm² and tumor size ≥5 cm, associated with death of disease (DoD; P = .010 and .016). Ki-67 expression ≥1% associated with DoD (P = .003) and death within 5 years (P = .031). Biomarkers stained tumor cases as follows: PDL-1 = 0%, PAX-5 = 0%, MET = 7.4%, paxillin = 41%, CRMP5 = 78%, p21 = 63%, p27 = 63%, EZH2 = 37%, and MASH1 = 59%. Overall ± staining did not associate with survival or grade. Cases with low CRMP5 H-scores (<80) associated with DoD (P = .002), while CRMP5 H-scores >80 associated with 10-year survival (P = .022). Cases with high MASH1 H-score (>100) associated with DoD (P = .021). Accurate grading and staging remain paramount in predicting clinical outcome. Biomarkers may have significance in subsets of patients and the use of these studies likely should be focused on a more personalize type of approach.

Novel Finding of Paired Box 5 (PAX5) Cytoplasmic Staining in Well-differentiated Rectal Neuroendocrine Tumors (Carcinoids) and Its Diagnostic and Potentially Prognostic Utility

Although nuclear immunostaining for paired box protein (PAX5) is widely used in practice, its cytoplasmic localization has not been evaluated. Recently we encountered cytoplasmic granular PAX5 staining in rectal well-differentiated neuroendocrine tumor (WD-NET) in the absence of nuclear staining. We investigated the specificity of this staining pattern for rectal NET (n=21) in comparison with 108 NETs, 1 WD rectal NET with elevated proliferation (WD-NET G3), and 40 poorly differentiated neuroendocrine carcinomas from the gastrointestinal and pancreatobiliary tract and liver. Representative tumor sections were subject to immunohistochemical stain for PAX5 antibody. Immunohistochemistry for 3 L-cell markers, glucagon-like peptide 1 and 2, and peptide YY, was performed on all rectal and appendiceal NETs and all other NETs with cytoplasmic PAX5 staining. Cytoplasmic PAX5 staining was observed in 90% (19/21) of rectal NET, 27% (3/11) of appendiceal, 14% (2/14) of pancreatic, 7% (2/29) of lung, 25% (3/12) metastatic NET in the liver, and 100% (1/1) of renal NET. No PAX5 cytoplasmic staining was seen in all grades of NET in other organs, rectal WD-NET G3, and all neuroendocrine carcinoma. L-cell marker staining was observed in all 21 (100%) rectal, in 3 of 3 (100%) PAX5-positive, and 1 of 7 (14%) PAX5-negative appendiceal NET. Cytoplasmic PAX5 staining is specific for rectal carcinoids. The sensitivity and specificity of PAX5 to detect L-cell type rectal carcinoids is 90% (19/21) and 100% (21/21), respectively. Cytoplasmic localization of the PAX5 protein may be utilized as a surrogate marker to detect L-cell type rectal carcinoids.

Diffuse large B-cell lymphoma carrying t(9;14)(p13;q32)/PAX5-immunoglobulin heavy chain gene is characterized by nuclear positivity of MUM1 and PAX5 by immunohistochemistry

We described four patients with diffuse large B-cell lymphoma (DLBCL) carrying t(9;14)(p13;q32) that places the PAX5 adjacent to the immunoglobulin heavy chain (IGH) gene. Ages ranged between 63 and 80, and three were female. One developed a nodal disease, and the other three involved extranodal organs. The lymphoma cells were CD10^- /BCL6^- /MUM1⁺ in three and CD10⁺ /BCL6⁺ /MUM1⁺ in one. BCL2 was weak or negative. All had t(9;14)(p13;q32), and three had additional 14q32/IGH translocations or +der(14)t(9;14)(p13;q32). Fluorescence in situ hybridization using the PAX5 break-apart probe showed that the locus was disrupted between the 5' and 3' probes or within the 5' probe. Immunohistochemistry (IHC) using a monoclonal antibody against PAX5 showed strong nuclear positivity in all four patients. Cell block IHC of a CD30⁺ DLBCL cell line, KIS-1, which carried the t(9;14)(p13;q32) and PAX5-IGH fusion gene, reproduced the CD10^- /BCL6^- /MUM1⁺ immunophenotype, low-level BCL2, and strong nuclear PAX5. Uniform nuclear positivity of MUM1 in all four cases and KIS-1 cells suggest that these lymphomas arose at a late stage of B-cell differentiation, where expression of PAX5 physiologically becomes downregulated. It is therefore possible that high-level PAX5 resulting from t(9;14)(p13;q32) at this stage of differentiation perturbs the plasma cell differentiation program initiated by PAX5 repression, thereby contributing to the development of a fraction of DLBCL.

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.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

Expression of PAX-5 in B Cell Hodgkin and Non Hodgkin Lymphoma

Background:

B-cell malignancies including Precursor B-cell lymphoblastic lymphoma/leukemia and Hodgkin Lymphoma show a wide spectrum of B-cell differentiation from early stage B-cell precursors to mature B-cells ending in terminal differentiation to plasma cells. Pan-B-cell antigens routinely used for the diagnosis of B-cell lymphoma, include CD19, CD20, CD22 and CD79a.PAX-5 protein, also known as B-cell-specific activation protein is a B-cell-specific transcription factor; essential for commitment and functional maintenance used in the diagnosis of B cell Hodgkin and non-Hodgkin lymphoma. PAX-5 show nuclear positivity in B cell lymphomas and moderate (dim) positivity in Hodgkinlymphoma Reed Sternberg cells make this marker ideal for diagnosing B cell malignances. Objective: To determine the expression of PAX-5 in B cell Hodgkin and non-Hodgkin Lymphoma in order to improve the diagnosis of B-cell lymphomas.

Methods:

In this Prospective study, all the cases of B cell lymphoma diagnosed at The Aga Khan University Hospital, Karachi from July 2010 to July 2011were included. A panel of Immunohistochemical stain was performed in all cases along with additional PAX- 5 stain with appropriate controls.

Results:

Total 125 cases were included. Hodgkin Lymphoma (Mixed cellularity) was the commonest B-cell lymphoma subtype, 32 (25%) cases. Other common subtypes included Hodgkin lymphoma (Nodular sclerosis subtype), diffuse large B-cell lymphoma and B lymphoblastic lymphoma.

Conclusion:

This study demonstrates that PAX-5 is the most sensitive and reliable immuhohistochemicalmarker in the diagnosis of B cell Hodgkin and non-Hodgkin lymphoma.

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.

Update on Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma. Incidence of MCC continues to rise, and risk factors include advanced age, pale skin, chronic sun exposure, and immune suppression. Diagnosing MCC utilizes a combination of morphology and immunohistochemistry. Merkel cell polyomavirus (MCPyV) is present in approximately 70-80% of MCCs and represents a key pathogenic driver in those MCCs. In contrast, MCPyV-negative MCCs arise through progressive accumulation of ultraviolet-light induced somatic mutations. Staging of MCC proceeds according to the American Joint Commission on Cancer (AJCC) 8th Edition, which utilizes features of the primary tumor together with regional lymph node(s) (clinically and/or pathologically detected) and/or distant metastases. Many potentially useful biomarkers have been studied to refine risk stratification in MCC. In recent years, the host immune infiltrate has been leveraged as immune checkpoint blockade has emerged as an efficacious mode of treatment for patients with advanced MCC.

Reviewing the current evidence supporting early B-cells as the cellular origin of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly malignant skin cancer characterized by early metastases and poor survival. Although MCC is a rare malignancy, its incidence is rapidly increasing in the U.S. and Europe. The discovery of the Merkel cell polyomavirus (MCPyV) has enormously impacted our understanding of its etiopathogenesis and biology. MCCs are characterized by trilinear differentiation, comprising the expression of neuroendocrine, epithelial and B-lymphoid lineage markers. To date, it is generally accepted that the initial assumption of MCC originating from Merkel cells (MCs) is unlikely. This is owed to their post-mitotic character, absence of MCPyV in MCs and discrepant protein expression pattern in comparison to MCC. Evidence from mouse models suggests that epidermal/dermal stem cells might be of cellular origin in MCC. The recently formulated hypothesis of MCC originating from early B-cells is based on morphology, the consistent expression of early B-cell lineage markers and the finding of clonal immunoglobulin chain rearrangement in MCC cells. In this review we elaborate on the cellular ancestry of MCC, the identification of which could pave the way for novel and more effective therapeutic regimens.

Expression of TIA1 and PAX5 in Classical Hodgkin Lymphoma at Initial Diagnosis May Predict Clinical Outcome

Although the expression of T-cell antigens and proteins associated with tumor-infiltrating T-lymphocytes (TILs), regulatory T cells (T-regs), and B-cell development have been evaluated in classical Hodgkin lymphoma (cHL), few studies correlate these proteins' expression patterns with clinical outcome. The purpose of this study was to evaluate proteins expressed in the Reed-Sternberg cells (RSCs) and TILs of cHLs at initial diagnosis to determine their prognostic significance. The expression of 12 proteins in RSCs and TILs from 88 diagnostic cHL biopsies was quantitated and correlated to overall survival (OS) and progression-free survival (PFS). CD2, CD3, CD4, CD5, CD7, CD25, PD1, TIA1, MUM1, and ZAP70 expression in RSCs did not correlate with OS or PFS, nor did programmed death 1 (PD1) expression in TILs. High numbers of TIA1-positive TILs (≥50%) correlated with OS (P=0.027), but not PFS (P=0.993) in univariate analysis. Expression of CD2, CD3, CD4, CD5, and/or TIA1 (6%) in RSCs was associated with lymphocyte-rich/mixed-cellularity subtype (P=0.032). High International Prognostic Score (IPS; P=0.036), and high stage (P=0.046) were independent predictors of worse PFS in univariate analysis. Low IPS (P=0.003) and nodular sclerosing subtype (P=0.022) were associated with better OS in univariate analysis. Only the IPS predicted OS in multivariate (P=0.009) analysis. High TIA1+ TILs correlated with worse clinical outcomes for cHLs, as did PAX5-RSCs (P=0.024), although only 2/74 cases were shown to be negative for this marker, suggesting that the tumor microenvironment and a transcription factor crucial for B-cell development are critical biological determinants of the disease course.

Pax-5 is a potent regulator of E-cadherin and breast cancer malignant processes

Pax-5, an essential transcription factor for B lymphocyte development, has been linked with the development and progression of lymphoid cancers and carcinoma. In contrast to B-cell cancer lesions, the specific expression signatures and roles of Pax-5 in breast cancer progression are relatively unknown. In the present study, we set out to profile Pax-5 expression in mammary tissues and elucidate the cellular and molecular roles of Pax-5 in breast cancer processes. Using immunohistology on mammary tissue arrays, Pax-5 was detected in a total of 298/306 (97.6%) samples tested. Interestingly, our studies reveal that Pax-5 inhibits aggressive features and confers anti-proliferative effects in breast carcinoma cells in contrast to its oncogenic properties in B cell cancers. More precisely, Pax-5 suppressed breast cancer cell migration, invasion and tumor spheroid formation while concomitantly promoting cell adhesion properties. We also observed that Pax-5 inhibited and reversed breast cancer epithelial to mesenchymal phenotypic transitioning. Mechanistically, we found that the Pax-5 transcription factor binds and induces gene expression of E-cadherin, a pivotal regulator of epithelialisation. Globally, we demonstrate that Pax-5 is predominant expressed factor in mammary epithelial cells. We also present an important role for Pax-5 in the phenotypic transitioning processes and aggressive features associated with breast cancer malignancy and disease progression.

Undifferentiated Nasopharyngeal Carcinoma Mimicking Hodgkin Lymphoma With CD30 Expression

The presence of CD30-expressing Hodgkin-like cells with a background of inflammation and eosinophils in a young adolescent is usually diagnostic of classical Hodgkin lymphoma. Herein we present the case of a 12-year-old boy presenting with enlarged cervical lymph node characterized by the presence of Hodgkin-like cells expressing CD30 and EBV-LMP1 with a Hodgkin-like background. The Hodgkin-like cells were negative for CD15, CD20, CD45, and Pax-5. The tumor cells, however, expressed several cytokeratins, confirming the diagnosis of an undifferentiated carcinoma nasopharyngeal type. This case highlights the importance of possessing a high index of suspicion when encountering lymph nodes with Hodgkin-like cells and a Hodgkin-like background, even with CD30 expression, as the differential can include undifferentiated carcinoma nasopharyngeal type.

Evaluation of Pax5 expression and comparison with BLA.36 and CD79αcy in feline non-Hodgkin lymphoma

Paired box gene 5 (Pax5) is a widely used B-cell marker for human and canine non-Hodgkin's lymphoma (nHL); however, in the literature there is only one case report using Pax5 in a cat B-cell lymphoma. The purposes of this study were to investigate the expression and detection of B-cell specific activator protein (BSAP) using a monoclonal anti-Pax5 antibody in feline nHL (FnHL) tissue samples to evaluate its diagnostic relevance as a B-cell marker. A total of 45 FnHL samples in 45 cats were evaluated. B-cell lymphoma was the most common immunophenotype (51.1%) for all the samples and T-cell the most common immunophenotype (64.3%) for the gastrointestinal (GI) form. Pax5 stained 82.6% of all B-cell lymphomas and no expression was found in any of the T-cell lymphomas. Anti-Pax5 antibody staining in FnHL is similar to that reported in human and canine counterparts and may offer an excellent B-cell marker in cats.

Oct2 and Bob1 are sensitive and specific markers in lineage determination of B cell lymphomas with no expression of conventional B cell markers

AIMS

Rare cases of B cell lymphomas do not express conventional B cell markers (CD20, CD79a and PAX5), and these types of lymphomas include anaplastic lymphoma kinase (ALK)-positive large B cell lymphoma, plasmablastic lymphoma, primary effusion lymphoma and the solid variant of primary effusion lymphoma, extracavitary human herpesvirus 8 (HHV8)-positive large B cell lymphoma. Establishing accurate diagnoses of these B cell lymphomas can be challenging, and often requires a large panel of immunohistochemical stains, molecular assays and cytogenetic studies. B cell-specific transcription factors, Oct2 and Bob1, have been shown to be expressed consistently in most, if not all, B cell lymphomas, and therefore we investigated the utility of Oct2 and Bob1 immunohistochemistry in lineage determination of the aforementioned B cell lymphomas.

METHODS AND RESULTS

We selected 34 cases of previously diagnosed B cell lymphomas with no or weak expression of CD20, CD79a and PAX5. Oct2 and Bob1 were positive in 74% (25 of 34) and 85% (29 of 34) of the cases, respectively. When we combined the results of these two immunostains, 94% (32 of 34) cases expressed at least one of these two markers. We also included 51 control cases of non-B cell neoplasms, and none of them expressed either Oct2 or Bob1.

CONCLUSIONS

Oct2 and Bob1 are very reliable in determining B cell lineage in the absence of expression of other pan-B cell markers, and it should provide great diagnostic benefit to include them both in a panel of immunohistochemistry to assess undifferentiated malignant neoplasms.

Diagnostic Utility of PAX5 in Hodgkin and Non-Hodgkin Lymphoma: A Study from Northern India

INTRODUCTION

PAX5 is an immunomarker of B-cell origin and useful in the diagnosis of lymphoma. There is hardly any study on PAX5 expression in Indian patients with lymphoma.

AIM

To evaluate the diagnostic utility of PAX5 as an adjunct immunohistochemical marker in the diagnosis of Hodgkin Lymphoma (HL) and Non-Hodgkin Lymphoma (NHL).

MATERIALS AND METHODS

Immunohistochemistry was performed against CD20, CD3, CD15, CD30, and PAX5 on formalin fixed paraffin embedded tissue of 71 cases of lymphoma and CD20, CD3 and PAX5 in control samples of reactive lymph nodes. Frequency, mean values, and percentage were calculated. Fisher's-exact test and test for analysis of variance were applied.

RESULT

For 24 cases of HL and 47 cases of NHL, the mean age of patients was 17.6±14.8 years and 44.1±21.6 years, respectively. The male: female ratio for both HL and NHL were 1.7:1. Among NHL cases, the numbers of B-cell and T-cell types were 39/47 (83%) and 8/47 (17%), respectively. In comparison to control samples, PAX5+ expression was seen in 23/24 (95.8%) cases of HL (p=1.000) and 32/39 (82%) cases of B-NHL (p=0.0834). All the cases of T-NHL showed negative expression of PAX5 (p<0.0001). Analysis of variance between NHL, HL and control samples was statistically significant (p<0.0001).

CONCLUSION

PAX5 staining between control samples and cases of classical HL and B-NHL was statistically not significant, whereas, statistically significant difference was observed with T-NHL. Thus, PAX5 may be used as an adjunct marker in the diagnosis of classical HL and B-NHL.

PAX5-expressing ALK-negative anaplastic large cell lymphoma with extensive extranodal and nodal involvement

A 55-year-old man with a history of well controlled HIV infection was admitted with acute renal impairment, peripheral oedema, constitutional symptoms, deranged liver function and hypercalcaemia. Core biopsies of a retroperitoneal mass demonstrated anaplastic lymphoma kinase (ALK) negative anaplastic large cell lymphoma (ALCL) with unusual Paired box 5 (PAX5) positivity. The same malignant cells were identifiable on urine cytology. Staging investigations revealed extensive nodal and extranodal disease including ALK negative ALCL involving the kidney and prostate, which has not previously been reported in the published literature.

Joint occurrence of Merkel cell carcinoma and non-Hodgkin lymphomas in four Nordic countries

The objective of this study was to assess the reciprocal association between non-Hodgkin lymphoma (NHL) and Merkel cell carcinoma (MCC) using the data of four Nordic Cancer Registries. Data for this study were drawn from the Danish, Finnish, Norwegian, and Swedish cancer registries. Standardized incidence ratios (SIRs) for MCC among NHL patients, and for NHL among MCC patients, were calculated. There were 109 838 individuals with NHL and 1411 individuals with MCC, of which 28 had joint occurrence of NHL and MCC. In 18 cases, NHL was diagnosed first, and in 10 cases, MCC was diagnosed first. The SIR for MCC after NHL was 4.34 (95% confidence interval 2.57-6.85). The SIR for NHL after MCC was 3.13 (1.50-5.77). Although the absolute frequency of joint occurrence of MCC and NHL is low, individuals suffering from one of the cancer forms have an increased risk of the other.

High incidence of Epstein-Barr virus (EBV)-positive Hodgkin lymphoma and Hodgkin lymphoma-like B-cell lymphoproliferations with EBV latency profile 2 in children with interleukin-2-inducible T-cell kinase deficiency

AIMS

Interleukin-2-inducible T-cell kinase (ITK) deficiency is an inherited T-cell deficiency characterized by the development of Epstein-Barr virus (EBV)-associated lymphoproliferations. We aimed to describe the histopathological features of lymphoproliferative processes arising in ITK deficiency, and to compare them with lymphoproliferations in otherwise immunocompromised patients.

METHODS AND RESULTS

We revised the histopathological diagnoses of 12 biopsies of lymphoproliferations from seven ITK-deficient children according to the World Health Organization criteria, and determined the EBV latency types and lytic activity by staining for EBV-encoded small RNA, latent membrane protein 1, EBV nuclear antigen 2, and ZEBRA. We found polymorphic and borderline polymorphic to monomorphic B-cell lymphoproliferations with variable contents in large cells (five cases), a Hodgkin-like B-cell proliferation (one case), and classic mixed-cellularity Hodgkin lymphoma (six cases). All cases (12/12) were EBV-positive. The Hodgkin lymphoma-like and Hodgkin lymphoma, and all but one polymorphic B-cell lymphoproliferation, showed EBV latency type 2, as observed in classic EBV-positive Hodgkin lymphoma.

CONCLUSIONS

The 100% EBV association, the high percentage of EBV-positive classic Hodgkin lymphoma and Hodgkin-like B-cell proliferations and the predominance of EBV latency type 2 even in polymorphic lesions are the main features of lymphoproliferations in patients with ITK deficiency, and suggest a unique pathomechanism of lymphomagenesis in this T-cell immunodeficiency.

Diagnostic Immunohistochemistry in Cutaneous Neoplasia: An Update

Immunohistochemistry (IHC) is an important adjunct in the diagnosis of neoplastic skin diseases. In addition to the many established IHC markers currently in use, new markers continue to emerge, although their general acceptance and routine application requires robust validation. Here, we summarize the most well-established and commonly used biomarkers along with an array of newer ones reported in the past several decades that either demonstrate or hold high clinical promise in the field of cutaneous pathology. We also highlight recent applications of novel IHC markers in melanoma diagnosis including genetic mutation status markers [e.g. BRAF (v-raf murine sarcoma viral oncogene homolog B) and NRAS (neuroblastoma RAS viral oncogene homolog)] and an epigenetic alteration marker (e.g. 5-hydroxymethylcytosine). We specifically focus on the role of IHC in the differential diagnosis of cutaneous lesions that fall under the following categories: melanoma, epidermal tumors with an intraepidermal epitheliomatous pattern, spindle cell lesions of the dermis, small round blue cell tumors of the dermis, and cutaneous adnexal tumors. While IHC is a valuable tool in diagnostic dermatopathology, marker selection and interpretation must be highly informed by clinical context and the histologic differential diagnosis. With rapid progress in our understanding of the genetic and epigenetic mechanisms of tumorigenesis, new IHC markers will continue to emerge in the field of diagnostic dermatopathology.

Merkel cell carcinoma of lymph node with unknown primary has a significantly lower association with Merkel cell polyomavirus than its cutaneous counterpart

Rare cases of Merkel cell carcinoma have been encountered in lymph nodes with unknown extranodal primary, which exhibit similar morphologic and immunophenotypic features to those in primary cutaneous Merkel cell carcinomas. However, it is uncertain whether the nodal Merkel cell carcinoma is a primary tumor of the lymph node or represents a metastasis from an occult or regressed extranodal lesion. To establish an accurate diagnosis of the nodal Merkel cell carcinoma can be challenging because of significant morphologic mimics, including lymphoblastic lymphoma and metastatic small cell carcinoma. Moreover, there is no consensus for a diagnostic term, and many different terms have been used, which can be confusing and may not fully reflect the nature of nodal Merkel cell carcinoma. In this study, we investigated the detailed clinicopathologic features of 22 nodal Merkel cell carcinomas, with comparison to 763 primary cutaneous cases retrieved from the literature. Overall, the nodal and cutaneous Merkel cell carcinomas shared similar clinical presentations, morphologic spectrum, and immunophenotype; both were mostly seen in elderly male with a typical neuroendocrine morphology. Most of cases expressed CK20, synaptophysin, and chromogranin A; and PAX5 and TdT were also positive in majority of cases. However, nodal Merkel cell carcinomas had a significantly lower association with Merkel cell polyomavirus than cutaneous cases (31% vs 76%, P=0.001). Therefore, these two entities may arise from overlapping but not identical biological pathways. We also recommend the use of the diagnostic term 'Merkel cell carcinoma of lymph node' to replace many other names used.

Merkel cell carcinoma - recent advances in the biology, diagnostics and treatment

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous carcinoma with neuroendocrine differentiation. Since recent discovery of MCCs strong association with Merkel cell polyomavirus (MCPyV), there has been a rapid increase in the understanding of the carcinomas genetics, molecular biology and pathogenesis. In our study, we reviewed recent advances and controversies concerning MCC histogenesis, epidemiology, diagnostic and prognostic markers. We analyzed the association of MCPyV with MCC and the possible new targets for therapy. We also examined English-based literature regarding MCC pathogenesis published between 2008 and 2013, which lead to a deeper understanding of the topic. Our study showed that the association of MCPyV strongly influences the course of MCC. Additionally, it has been shown that a immunological response to MCPyV may in the future give hope to identify new therapeutic strategies in treatment of this fatal malignancy. This article is part of a Directed Issue entitled: Rare Cancers.

Epigenetic-mediated tumor suppressor genes as diagnostic or prognostic biomarkers in gastric cancer

Gastric cancer is believed to result in part from the accumulation of multiple genetic and epigenetic alterations leading to oncogene overexpression and tumor suppressor loss. Tumor suppressor genes are inactivated more frequently by promoter methylation than by mutation in gastric cancer. Identification of genes inactivated by promoter methylation is a powerful approach to discover novel tumor suppressor genes. We have previously identified tumor suppressor genes in gastric cancer by genome-wide methylation screening. The biological functions of these genes are related to cell adhesion, ubiquitination, transcription, p53 regulation and diverse signaling pathways. Some of the tumor suppressor genes are of particular clinical importance as they can be used as predictive biomarkers for early diagnosis or ongoing prognosis of gastric cancer.

Early B-cell differentiation in Merkel cell carcinomas: clues to cellular ancestry

Merkel cell carcinoma (MCC) is a highly malignant neuroendocrine nonmelanoma skin cancer, which is associated with the Merkel cell polyoma virus (MCPyV). Recently, expression of the terminal deoxynucleotidyl transferase (TdT) and the paired box gene 5 (PAX 5) has been consistently reported in the majority of MCCs. We tested 21 MCCs for the expression of MCPyV, TdT, PAX5, IgG, IgM, IgA, kappa, and lambda by immunohistochemistry and assessed IgH and Igk rearrangement in all 21 MCCs. All of the MCCs revealed specific expression of PAX5 and 72.8% of the MCCs expressed TdT. In addition, most of the MCCs revealed specific expression of one or more Ig subclasses and kappa or lambda. One MCC did reveal monoclonal IgH and Igk rearrangement next to two other MCCs showing Igk rearrangement. As coexpression of TdT and PAX5 under physiologic circumstances is restricted to pro/pre- and pre-B cells we propose, on the basis of our results, that the cell of origin of MCCs is a pro/pre- or pre-B cell rather than the postmitotic Merkel cells. MCPyV infection and transformation of pro-/pre-B cells are likely to induce the expression of simple cytokeratins as has been shown for SV40 in other nonepithelial cells. This model of cellular ancestry of MCCs might impact therapy and possibly helps to understand why approximately 20% of MCCs are MCPyV-negative.

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.

Epigenetic inactivation of paired box gene 5, a novel tumor suppressor gene, through direct upregulation of p53 is associated with prognosis in gastric cancer patients

Using genome-wide methylation screening, we identified that paired box gene 5 (PAX5) is involved in human cancer development. However, the function of PAX5 in gastric cancer (GC) development is largely unclear. We analyzed its epigenetic inactivation, biological functions and clinical application in GC. PAX5 was silenced in seven out of eight GC cell lines. A significant downregulation was also detected in paired gastric tumors compared with adjacent non-cancerous tissues. The downregulation of PAX5 was closely linked to the promoter hypermethylation status and could be restored with demethylation treatment. Ectopic expression of PAX5 in silenced GC cell lines (AGS and BGC823) inhibited colony formation and cell viability, arrested cell cycle, induced apoptosis, suppressed cell migration and invasion and repressed tumorigenicity in nude mice. Consistent with the induction of apoptosis by PAX5 in vitro, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) staining showed significantly enhanced apoptotic cells in PAX5-expressed tumors compared with the vector control tumors. On the other hand, knockdown of PAX5 by PAX5-short hairpin RNA increased the cell viability and proliferation. The anti-tumorigenic function of PAX5 was revealed to be mediated by upregulating downstream targets of tumor protein 53 (p53), p21, BCL2-associated X protein, metastasis suppressor 1 and tissue inhibitors of metalloproteinase 1, and downregulating BCL2, cyclin D1, mesenchymal-epithelial transition factor (MET) and matrix metalloproteinase 1. Immunoprecipitation assay demonstrated that PAX5 directly bound to the promoters of p53 and MET. Moreover, PAX5 hypermethylation was detected in 77% (144 of 187) of primary GCs compared with 10.5% (2/19) of normal gastric tissues (P<0.0001). GC patients with PAX5 methylation had a significant poor survival compared with the unmethylated cases as demonstrated by Cox regression model and log-rank test. In conclusion, PAX5 is a novel functional tumor suppressor in gastric carcinogenesis. Detection of methylated PAX5 can be utilized as an independent prognostic factor in GC.

An Immunohistochemical Panel to Differentiate Metastatic Breast Carcinoma to Skin From Primary Sweat Gland Carcinomas With a Review of the Literature

Context.—Approximately 25% of patients with breast cancer develop cutaneous metastases. Sweat gland carcinomas (SGCs) account for about 0.05% of all cutaneous neoplasms. Cutaneous metastases of breast carcinoma (CMBCs) (especially the ductal type) can be difficult to distinguish from SGCs. Treatment and prognoses for these 2 types of tumors differ radically, making accurate histologic diagnosis crucial. Although a few studies attempt to differentiate these entities employing immunohistochemical (IHC) studies (some of which we review here), to date, no panel of IHC stains exists, to our knowledge, to distinguish these entities.

Objective.—To devise a panel of IHC stains to distinguish CMBC from SGC.

Design.—Twelve cases of ductal CMBCs (11 not otherwise specified type, and 1 basal phenotype), 11 cases of SGCs (5 eccrine carcinomas, 3 porocarcinomas, and 3 microcystic adnexal carcinomas), 2 benign sweat gland neoplasm cases, and 2 primary breast cancer cases were retrieved and analyzed with the following IHC panel: mammaglobin, gross cystic disease fluid protein (GCDFP) 15, p63, basal cytokeratins (CK5, CK14, and CK17), androgen receptor, and PAX5.

Results.—The p63 was only weakly expressed in 1 of 12 CMBC cases (8.3%), whereas it was strongly expressed in 10 of 11 SGC cases (90.9%) (P &lt; .001). Basal cytokeratins demonstrated a similar immunoprofile in the SGC group, with 10 of 11 cases (90.9%) expressing all 3 markers, and a variable immunoprofile in the CMBC group with 0% (CK14) (P &lt; .001) to 16.7% (2 of 12 cases; CK5 and CK17) (P &lt; .001) expression. Mammaglobin was expressed in 8 of 12 cases (66.7%) of CMBC.

Conclusions.—Together, these 5 IHC stains were combined to make a panel that was 100% sensitive and 91% specific in distinguishing between CMBC and SGC.

Characterization of a New Monoclonal Antibody Against PAX5/BASP in 1525 Paraffin-embedded Human and Animal Tissue Samples

INTRODUCTION

We describe the newly generated DAK-PAX5 monoclonal antibody raised against a fixation-resistant epitope of the human PAX5/BSAP molecule.

MATERIALS AND METHODS

Following Western-blot, absorption, and chess-board titration tests, and optimization of antigen-retrieval and detection methods, DAK-Pax5 was used in parallel with a reference antibody (clone 24) on tissue micro-arrays (TMAs) constructed from normal human and animal tissues and from hematologic and nonhematologic human malignancies. Such TMAs were also tested with an anti-PAX2 antibody.

RESULTS

DAK-Pax5 reacted with normal human and animal B-cells and with 460/473 B-cell non-Hodgkin lymphomas (B-NHLs). All plasmacytomas/plasmablastic tumors (n=13) and T/NK-cell neoplasms (n=264) turned out consistently negative as did acute myelogenous leukaemias (n=19) except 2 carrying t(8;21). Positivity was found in 6/6 and 155/169 lymphocyte predominant and classical HLs, respectively, although the staining intensity varied through cases. Among 521 nonhematologic malignancies, DAK-Pax5 reacted with 22/399 carcinomas (4/11 neuroendocrine, 2/4 Merkel-cell, 4/21 prostatic, 1/11 urothelial, 1/26 renal, 2/12 cervical squamous-cell, 3/13 ovarian, and 5/75 colonic). When compared with clone 24, DAK-Pax5 produced a stronger positivity in most if not all B-NHLs and HLs. No cross-reactivity with the anti-PAX2 antibody was recorded.

DISCUSSION

DAK-Pax5 represents a new reliable tool for diagnostics and research.

PAX-5: a valuable immunohistochemical marker in the differential diagnosis of lymphoid neoplasms

OBJECTIVE

Undifferentiated tumors and hematolymphoid neoplasms can be diagnostically challenging due to potential overlap of morphologic features and variant antigen expression. PAX-5, a transcription factor expressed throughout B-cell maturation, is detected in most B-cell neoplasms including those that lack expression of mature B-cell markers, such as classical Hodgkin lymphoma (cHL), B-lymphoblastic leukemia and B-cell lymphomas following rituximab therapy. The lack of PAX-5 expression in most CD30-positive non-hematopoietic malignancies (embryonal carcinoma and seminoma) and T-cell lymphomas, such as anaplastic large cell lymphoma (ALCL), suggests that the absence of PAX-5 may be used to confirm non-B-cell lineage. The goal of this study was to retrospectively assess PAX-5 immunoreactivity in diagnostic samples of hematolymphoid and other non-hematopoietic malignancies.

DESIGN

Diagnostic lymph node, decalcified core bone marrow biopsies and tissue sections from 111 archived paraffin-embedded tissue blocks and a tissue lymphoma microarray were immunostained using a monoclonal antibody to PAX-5. The corresponding hematoxylin and eosin stained tissue sections and additional immunostains were simultaneously evaluated. PAX-5 immunoreactivity in neoplastic cells was scored as positive or negative. This study was exempted by the Institutional Review Board for Human Research.

RESULTS

Nuclear PAX-5 immunoreactivity was detected in 88% (36/41) of Hodgkin lymphoma, all cases of diffuse large B-cell lymphoma (n=72), small B-cell lymphomas (n=5), B-lymphoblastic leukemia/lymphoma and mixed phenotype acute leukemia with B-cell lineage (n=5). PAX-5 was not detected in ALCL (n=22), T-cell lymphoblastic leukemia/lymphoma, mixed phenotype acute leukemia with T-cell lineage (n=5), acute myeloid leukemia (n=4), carcinoid tumors with typical morphology (n=5), melanoma (n=3), and undifferentiated/metastatic tumors (n=8). Non-neoplastic bone marrow sections showed scattered nuclear staining in small B-cell lymphocytes/hematogones. The detection of PAX-5 immunoreactivity resulted in the reclassification of two cases of ALCL to cHL.

CONCLUSION

Overall, our results demonstrate that including PAX-5 in a panel with other immunomarkers helps establish B-cell lineage and increases diagnostic yield.

PAX5-positive T-cell anaplastic large cell lymphomas associated with extra copies of the PAX5 gene locus

Cell lineage is the major criterion by which lymphomas are classified. Immunohistochemistry has greatly facilitated lymphoma diagnosis by detecting expression of lineage-associated antigens. However, loss or aberrant expression of these antigens may present diagnostic challenges. Anaplastic large cell lymphoma is a T-cell lymphoma that shows morphologic and phenotypic overlap with classical Hodgkin's lymphoma, which is a tumor of B-cell derivation. Staining for the B-cell transcription factor, paired box 5 (PAX5), has been suggested to be helpful in this differential, as it is positive in most classical Hodgkin's lymphomas, but absent in anaplastic large cell lymphomas. In this study we report four systemic T-cell anaplastic large cell lymphomas that were positive for PAX5 by immunohistochemistry, with weak staining intensity similar to that observed in classical Hodgkin's lymphoma. All diagnoses were confirmed by a combination of morphologic, phenotypic, and molecular criteria. Three cases were anaplastic lymphoma kinase (ALK) negative and one was ALK positive. PAX5 immunohistochemistry was negative in 198 additional peripheral T-cell lymphomas, including 66 anaplastic large cell lymphomas. Unexpectedly, although PAX5 translocations were absent, all evaluable PAX5-positive anaplastic large cell lymphomas showed extra copies of the PAX5 gene locus by fluorescence in situ hybridization (FISH). In contrast, only 4% of PAX5-negative peripheral T-cell lymphomas had extra copies of PAX5. We conclude that aberrant expression of PAX5 occurs rarely in T-cell anaplastic large cell lymphomas, and may be associated with extra copies of the PAX5 gene. PAX5-positive lymphomas with morphologic features overlapping different lymphoma types should be evaluated with an extensive immunohistochemical panel and/or molecular studies to avoid diagnostic errors that could lead to inappropriate treatment. As PAX5 overexpression causes T-cell neoplasms in experimental models, PAX5 may have contributed to lymphomagenesis in our cases.

PAX5 expression in nonhematopoietic tissues. Reappraisal of previous studies

The Pax gene family encodes transcription factors with similar structures but distinctive roles in development and with limited expression in adult tissues. Reexpression of PAX proteins is frequently observed in human cancers, reflecting recapitulation of embryologic or developmental function. Defining expression of PAX family members is important in the immunohistochemical differential diagnosis of cancer, understanding oncogenesis, and defining targets for therapy. Immunostaining for PAX5 has become a commonly used technique in differential diagnosis of B-lineage hematologic malignancies. In seeking to define the range and degree of expression of PAX5 in nonhematologic pediatric cancers by immunohistochemical analysis with the anti-PAX5 monoclonal antibody routinely used in research and diagnosis, we observed strong immunostaining in a number of malignant tissues, including Wilms tumor. The pattern of expression of PAX5 in Wilms tumor was found to be identical to that of PAX2, raising the possibility of antibody cross-reactivity. This was subsequently confirmed by Western blotting and immunostaining of transfected cells and quantitative reverse transcriptase-polymerase chain reaction. Since the same PAX5 monoclonal antibody has been used consistently in the literature, these findings indicate a need for reappraisal of published PAX5 immunostaining results.

PAX5 activates the transcription of the human telomerase reverse transcriptase gene in B cells

Telomerase is an RNA-dependent DNA polymerase that synthesizes telomeric DNA. Its activity is not detectable in most somatic cells but it is reactivated during tumorigenesis. In most cancers, the combination of hTERT hypermethylation and hypomethylation of a short promoter region is permissive for low-level hTERT transcription. Activated and malignant lymphocytes express high telomerase activity, through a mechanism that seems methylation-independent. The aim of this study was to determine which mechanism is involved in the enhanced expression of hTERT in lymphoid cells. Our data confirm that in B cells, some T cell lymphomas and non-neoplastic lymph nodes, the hTERT promoter is unmethylated. Binding sites for the B cell-specific transcription factor PAX5 were identified downstream of the ATG translational start site through EMSA and ChIP experiments. ChIP assays indicated that the transcriptional activation of hTERT by PAX5 does not involve repression of CTCF binding. In a B cell lymphoma cell line, siRNA-induced knockdown of PAX5 expression repressed hTERT transcription. Moreover, ectopic expression of PAX5 in a telomerase-negative normal fibroblast cell line was found to be sufficient to activate hTERT expression. These data show that activation of hTERT in telomerase-positive B cells is due to a methylation-independent mechanism in which PAX5 plays an important role.

Expression profiling of transcription factors in B- or T-acute lymphoblastic leukemia/lymphoma and burkitt lymphoma: usefulness of PAX5 immunostaining as pan-Pre-B-cell marker

The optimal use of transcription factors to determine B-lineage specificity in B-acute lymphoblastic leukemia/lymphoma (B-ALL) has not been fully investigated. We undertook an extensive immunohistochemical study of a panel of B-cell transcription factors in B- and T-ALL and Burkitt lymphoma to evaluate those with the best specificity and sensitivity. Tissue microarrays were constructed from 34 B-ALL, 19 T-ALL, and 30 Burkitt lymphoma samples. All 34 (100%) cases of B-ALL expressed PAX5; 32 (94%), BOB.1; 33 (97%), PU.1; 29 (85%), CD79a; 27 (79%), CD22; 2 (6%), CD20; 9 (26%), OCT-2; and 3 (9%), MUM1. Burkitt lymphoma cases were positive for PAX5 (30/30 [100%]), BOB.1 (27/30 [90%]), PU.1 (23/30 [77%]), CD79a (29/30 [97%]), CD22 (14/30 [47%]), CD20 (30/30 [100%]), OCT-2 (23/30 [77%]), and MUM1 (5/30 [17%]). T-ALLs were only positive for PU.1 (15/19 [79%]) and BOB.1 (12/19 [63%]). PAX5 demonstrated better specificity for B-lineage determination than BOB.1 and PU.1 and better sensitivity than CD79a, CD22, and CD20. These findings suggest that PAX5 has the greatest diagnostic usefulness and lineage determination in B-ALL, especially in cases with an inadequate specimen for flow cytometric analysis.

PAX immunoreactivity identifies alveolar rhabdomyosarcoma

PAX5 is a member of the paired box transcription factors involved in development and its expression has been well characterized among hematopoietic malignancies of B-cell lineage. Its expression has also been reported in a subset of neuroendocrine carcinomas, urothelial tumors, Merkel cell carcinoma, glioblastoma, and neuroblastoma cell lines. As such, we sought to assess it as a diagnostic marker in the evaluation of pediatric small round blue cell tumors. Tumors selected for evaluation included embryonal rhabdomyosarcoma (55 cases), alveolar rhabdomyosarcoma (ARMS) (51 cases), neuroblastoma (22 cases), Wilms tumor (18 cases), Ewing Family of Tumors (11 cases), lymphoblastic lymphoma (8 cases), hepatoblastoma (6 cases), and granulocytic sarcoma (3 cases) as either cores in a tissue microarray or whole mount sections. All cases were immunostained using an antibody directed toward PAX5 and immunoreactivity was scored semiquantitatively according to percentage of nuclear staining. As expected, all B-cell lymphoblastic lymphomas were strongly immunoreactive against PAX5. Additionally, all Wilms tumors showed staining of variable intensity, most intensely in the epithelial component. Of the rhabdomyosarcoma cases, 34 of 51 (67%) ARMS were immunoreactive whereas none of the 55 embryonal rhabdomyosarcoma cases stained. No other tumor type on the array was immunoreactive toward PAX5. Genetic information was available on 7 ARMS, 5 of which had characteristic translocations involving PAX genes, either t(2:13) or t(1;13). Of the translocation-positive cases, all showed nuclear reactivity toward PAX5, and both the translocation-negative cases did not. Possible explanations of PAX5 staining include aberrant expression of the PAX5 transcription factor, PAX5 expression in normal tissue at the time the tumors most closely recapitulates in development or crossreactivity with another member of the PAX family. PAX3 and PAX7 fusion genes characterize the majority of ARMS making crossreactivity with these proteins an attractive theory, and suggest that PAX5 immunoreactivity may be specific for translocation-positive ARMS. Further study in a larger series of rhabdomyosarcomas is warranted to assess the sensitivity and specificity of PAX5 immunoreactivity for the ARMS variant.

PAX5 is expressed in small-cell lung cancer and positively regulates c-Met transcription

PAX5 is a nuclear transcription factor required for B cell development, and its expression was evaluated in upper aerodigestive malignancies and pancreatic cancer by immunoblotting. The PAX5 protein expression was relatively strong in small-cell lung cancer (SCLC, 11/12); however, its expression was not detected in non-SCLC (NSCLC, n=13), mesothelioma (n=7), pancreatic (n=6), esophageal (n=6) and head and neck cancer cell lines (n=12). In comparison, PAX8 and PAX3 expressions were absent or non-detectable in SCLC cell lines; however, PAX8 was expressed in most of the tested NSCLC cell lines (13/13) and also frequently in all the other cell lines. We also detected frequent expressions of PAX2 and PAX9 protein in the various cell lines. Utilizing neuroendocrine tumor samples, we found that the frequency as well as the average intensity of the expression of PAX5 increased from pulmonary carcinoid (9%, moderate and strong PAX5 expression, n=44), to large-cell neuroendocrine carcinoma (LCNC, 27%, n=11) to SCLC (33%, n=76). FISH analysis revealed no translocations of the PAX5 gene, but polyploidy in some SCLC tumor tissues (6/37). We determined that PAX5 could regulate the transcription of c-Met using luciferase-coupled reporter and chromatin immunoprecipitation analysis. In addition, the phospho-c-Met (active form) and PAX5 were both localized to the same intra-nuclear compartment in hepatocyte growth factor treated SCLC cells and interacted with each other. Finally, we determined the therapeutic translational potential of PAX5 using PAX5 knockdown SCLC cells in conjunction with Topoisomerase 1 (SN38) and c-Met (SU11274) inhibitors. Loss of endogenous PAX5 significantly decreased the viability of SCLC cells, especially when combined with SN38 or SU11274, and maximum effect was seen when both inhibitors were used. Therefore, we propose that PAX5 could be an important regulator of c-Met transcription and a potential target for therapy in SCLC.