Expression of bcl-6 and CD10 in primary mediastinal large B-cell lymphoma: evidence for derivation from germinal center B cells?

Aggressive Mediastinal Lymphomas

The mediastinum contains essentially all major intrathoracic organs except for the lungs. A variety of both benign and malignant tumors can involve the mediastinum, of which lymphoma is the most common malignancy. Compared to secondary mediastinal involvement by systemic lymphomas, primary mediastinal lymphomas are less common with several specific entities that are mainly confined to mediastinal lymph nodes, and/or thymus. This review will summarize the clinical, histologic, immunophenotypic and molecular genetic features of the most common and most aggressive primary mediastinal lymphomas as well as provide suggested immunohistochemistry panels and differential diagnoses.

A comprehensive review of the literature on CD10: its function, clinical application, and prospects

CD10, a zinc-dependent metalloprotease found on the cell surface, plays a pivotal role in an array of physiological and pathological processes including cardiovascular regulation, immune function, fetal development, pain response, oncogenesis, and aging. Recognized as a biomarker for hematopoietic and tissue stem cells, CD10 has garnered attention for its prognostic potential in the progression of leukemia and various solid tumors. Recent studies underscore its regulatory significance and therapeutic promise in combating Alzheimer's disease (AD), and it is noted for its protective role in preventing heart failure (HF), obesity, and type-2 diabetes. Furthermore, CD10/substance P interaction has also been shown to contribute to the pain signaling regulation and immunomodulation in diseases such as complex regional pain syndrome (CRPS) and osteoarthritis (OA). The emergence of COVID-19 has sparked interest in CD10's involvement in the disease's pathogenesis. Given its association with multiple disease states, CD10 is a prime therapeutic target; inhibitors targeting CD10 are now being advanced as therapeutic agents. This review compiles recent and earlier literature on CD10, elucidating its physicochemical attributes, tissue-specific expression, and molecular functions. Furthermore, it details the association of CD10 with various diseases and the clinical advancements of its inhibitors, providing a comprehensive overview of its growing significance in medical research.

Stromal CD10 expression in gastric adenocarcinoma

Gastric adenocarcinoma is a malignant neoplasm of the gastric mucosa composed of neoplastic cells and supporting stroma as with any neoplasm. Stromal myofibroblasts have an essential role in creating the tumor-promoting environment. They express certain substances, such as CD10. In this study, stromal CD10 expression was investigated by immunohistochemistry in gastric carcinoma, and its association with specific clinicopathological parameters was analyzed. Formalin-fixed paraffin-embedded blocks of 80 gastric adenocarcinoma cases were collected retrospectively in a private laboratory of the Rizgary Teaching Hospital for 2 years (January 2018–January 2020). Finally, the immunohistochemical study of CD10 expression in stromal cells was performed. According to the results, stromal CD10 immunoreactivity was detected in 15% of the cases. Furthermore, a statistically significant correlation was observed between stromal CD10 and the tumor type (P=0.015). However, no statistically significant relationship was identified between stromal CD10 expression and patients' age, gender, lymphovascular invasion, lymph node status, and tumor stage and grade. The results suggest a statistically significant positive correlation between stromal CD10 expression and tumor type.

How I Diagnose Primary Mediastinal (Thymic) Large B-Cell Lymphoma

OBJECTIVES

Primary mediastinal (thymic) large B-cell lymphoma (PMBL) is an uncommon large B-cell neoplasm recognized by the World Health Organization as a distinct entity on the basis of its unique clinical features, histogenesis, phenotype, and pathogenetic mechanisms. The diagnosis of PMBL can be challenging because of features that may overlap with other (Hodgkin and non-Hodgkin) lymphoma types. This review describes our approach to the diagnosis of PMBL.

METHODS

Two cases are presented to illustrate how we diagnose PMBL and separate PMBL from related histologic and biological mimickers, such as Hodgkin lymphoma and gray zone lymphoma.

RESULTS

A diagnosis of PMBL requires correlation of morphology and immunophenotype with clinical and staging data. Gene expression analysis is not typically performed in clinical labs but has expanded our understanding of the functional pathways underlying this disease and helped identify biomarkers that can be translated to diagnostic practice and possibly to future therapeutic options.

CONCLUSIONS

PMBL and closely related entities can pose diagnostic challenges. It is important to understand the borders between PMBL and other closely related lymphoma types so that patients receive successful primary treatment with curative intent.

Mediastinal Lymphoproliferative Disorders

Lymphoproliferative disorders comprise 50% to 60% of all mediastinal malignancies in both children and adults. Primary mediastinal involvement is rare (∼5%), whereas secondary mediastinal involvement by systemic disease is more common (10% to 25%). Primary mediastinal disease is defined as involvement by a lymphoproliferative disorder of mediastinal lymph nodes, the thymus, and/or extranodal mediastinal organs without evidence of systemic disease at presentation. In this review, the clinical, radiologic, histopathologic, immunohistochemical, and genetic features of some of the most characteristic mediastinal lymphoproliferative disorders are presented. The entities discussed here include: classic Hodgkin lymphoma with emphasis on nodular sclerosis and mixed cellularity types, and non-Hodgkin lymphomas, including primary mediastinal (thymic) large B-cell lymphoma, mediastinal gray zone lymphoma, mediastinal diffuse large B-cell lymphoma, thymic marginal zone lymphoma, mediastinal plasmacytoma, T-lymphoblastic lymphoma, and anaplastic large cell lymphoma. Although not a malignant process, hyaline vascular Castleman disease is also discussed here as this disorder commonly involves the mediastinum. Despite multiple advances in hematopathology in recent decades, the day-to-day diagnosis of these lesions still requires a morphologic approach and a proper selection of immunohistochemical markers. For this reason, it is crucial for general pathologists to be familiar with these entities and their particular clinicoradiologic presentation.

Primary Mediastinal (Thymic) Large B-Cell Lymphoma: Fidelity of Diagnosis Using WHO Criteria

PURPOSE

Diagnosing primary mediastinal (thymic) large B-cell lymphoma (PMBCL) is challenging because it is a clinicopathologic entity that shares characteristics with other lymphomas and lacks pathognomonic features. We sought to investigate the fidelity between a working diagnosis of PMBCL at our institution and the clinicopathologic criteria established within the 2017 World Health Organization (WHO) classification.

PATIENTS AND METHODS

Medical records and archived tissue of patients treated for stage I-II PMBCL from 1998 to 2018 were retrospectively reviewed for clinical and pathologic conformity with current WHO criteria. Disease was characterized as definitely PMBCL if all of the following were present: anterior mediastinal mass with or without lymph node involvement, no extranodal disease, B-cell antigen expression, Epstein-Barr virus negativity, and at least one supportive feature: female gender under age 40, bulky primary tumor, CD30 weakly positive, compartmentalizing alveolar fibrosis, lack of surface immunoglobulin expression, and MUM1 or CD23 positivity. Disease without supportive features or other pathologic findings more suggestive of other entities was characterized as equivocal for PMBCL. Lack of an anterior mediastinal mass, presence of distant lymph node involvement or extranodal disease, lack of B-cell antigen expression, or Epstein-Barr virus positivity were characterized as definitely not PMBCL. Clinical management and outcomes were also assessed.

RESULTS

Of 63 patients treated for presumed stage I-II PMBCL, 58 (92%) met the criteria for PMBCL. The most common reason for a discordant diagnosis was lack of an anterior mediastinal mass (n = 3). Two additional patients were characterized as having disease equivocal for PMBCL. In retrospect, one patient most likely had a mediastinal gray zone lymphoma due to CD15 positivity and another diffuse large B cell, not otherwise specified, at pathologic review. Five-year progression-free and overall survival were 67% (95% confidence interval, 54-77) and 81% (95% confidence interval, 68-89), respectively, for all patients.

CONCLUSION

Despite the complexity of the clinicopathologic criteria of PMBCL, most patients (92%) who were treated for stage I-II PMBCL at our institution appear to have been accurately diagnosed.

Infectious mononucleosis mimicking Epstein-Barr virus positive diffuse large B-cell lymphoma not otherwise specified

The Epstein–Barr virus (EBV) causes infectious mononucleosis (IM). In the case of atypical presentation, lymph node and tonsillar biopsies are required to rule out lymphoma. Here, we discuss an 83-year-old male who presented with findings suggestive of diffuse large B-cell lymphoma, which was later ruled out in favor of IM. The distinction between IM and lymphomas is quite challenging due to the extensive overlap between the two diseases. Various studies have demonstrated that EBV-positive diffuse large B-cell lymphoma mimics IM due to large B-cell proliferation in acute EBV infection. We suggest testing for acute EBV infection in addition to utilizing advanced testing to confirm IM in patients with atypical infection, to avoid misdiagnosis leading to inappropriate treatment.

Primary Mediastinal Nodal and Extranodal Non-Hodgkin Lymphomas: Current Concepts, Historical Evolution, and Useful Diagnostic Approach: Part 1

Primary mediastinal non-Hodgkin lymphomas (PM-NHLs) represent ~5% of all NHLs and comprise lymphomas of B-cell and T-cell origin. PM-NHLs are defined as involvement of mediastinal lymph nodes, thymus, and/or mediastinal organs (heart, lung, pleura, pericardium) by NHL without evidence of systemic disease at presentation. The clinical scenario is variable and depends on the lymphoma subtype. The radiologic presentation is also variable ranging from a mediastinal mass with or without superior vena cava syndrome, a pleural or a cardiac mass associated with an effusion, or as an effusion only. The diagnosis of PM-NHLs can only be established by microscopic evaluation, and therefore, general pathologists should be aware of these tumors and familiar with their diagnostic approach. The most common anterior mediastinal NHLs (90% to 95%) are primary mediastinal large B-cell lymphoma and T lymphoblastic lymphoma. Thymic marginal zone lymphoma and mediastinal gray zone lymphoma are very rare. The remainder PM-NHLs involving middle or posterior mediastinum include diffuse large B-cell lymphoma (DLBCL) and rare cases of T-cell lymphoma, including anaplastic large cell lymphoma and breast implant-associated anaplastic large cell lymphoma extending to the anterior mediastinum. Primary pleural and cardiac NHLs are mostly DLBCLs. Other rare subtypes of PM-NHLs include DLBCL associated with chronic inflammation/pyothorax-associated lymphoma, fibrin-associated DLBCL (both EBV), and pleural and/or pericardial primary effusion lymphoma (HHV-8/EBV). We review the historical aspects, epidemiology, clinico-radiologic features, histopathology, immunohistochemistry, differential diagnosis, and relevant cytogenetic and molecular features of PM (thymic) LBCL, PM "nonthymic" DLBCL, BCL, unclassifiable, with features intermediate between DLBCL and classic Hodgkin lymphoma (mediastinal gray zone lymphoma), DLBCL associated with chronic inflammation (pyothorax-associated lymphoma), fibrin-associated DLBCL, and primary effusion lymphoma. This review represents the first part of 2 manuscripts covering PM-NHLs.

[Primary mediastinal large B-cell lymphoma in women: about five cases]

Primary mediastinal large B-cell lymphoma (PMBL) is a lymphoma occurring in the anterior mediastinum starting from the cells B of the thymique medullary zone. This is a rare entity characterized by epidemiological, clinical and evolutionary peculiarities as well as by pathological and immunohistochemical peculiarities. We report a case series of 5 patients with diagnosed PMBL hospitalized in Pulmonology Department of Ibn Sina Hospital between January 2012 and May 2016. The average age was 34 years, the median of consultation time was 2 months. Reported symptoms were dyspnea, chest pain, dry cough; two patients suffered from superior vena cava syndrome. LDH level was high in 4 patients. Thoracic imaging showed an anterior mediastinal tissue processing in 5 patients. Histological diagnosis was based on ultrasound-guided transparietal puncture biopsy in 5 patients. The contribution of immunohistochemistry was decisive in all cases. Patients were sent to the National Institute of Oncology for therapeutic management. PMBL prognosis is reserved, it most commonly occurs in young women, which increases the need of aggressive therapy to improve survival rate.

Surface Light Chain Expression in Primary Mediastinal Large B-Cell Lymphomas by Multiparameter Flow Cytometry

OBJECTIVES

Primary mediastinal large B-cell lymphoma (PMLBL) is an aggressive B-cell lymphoma typically localized to the mediastinum. To date, no study has undertaken a comprehensive analysis of this entity by multiparameter flow cytometry.

METHODS

Cases of PMLBL with diagnostic flow cytometry were identified from pathology databases of Boston Children's Hospital, Brigham and Women's Hospital, and Stanford Hospital.

RESULTS

Most of these patients with PMLBL were women with a median age of 30 years who had stage 1 disease that lacked bone marrow involvement. By flow cytometry, 50% of all PMLBLs showed restricted surface immunoglobulin expression. When comparing patients with PMLBL by the absence or presence of surface light chain immunoglobulins, no differences were seen in the morphologic appearance; expression of CD23, CD30, or CD10; age at presentation; or clinical stage (P > .5 for all). In addition, both groups showed similarly good survival outcomes and were alive at last follow-up (11/14 [79%]; P = .542).

CONCLUSIONS

This multi-institutional study demonstrates that 50% of PMLBLs can present with clonal surface light chain expression and that PMLBL is more immunophenotypically diverse than previously described. Furthermore, our findings suggest that the absence or presence of surface light chains should not be used as criteria for diagnosis in this disease.

Primary mediastinal lymphoma: diagnosis and treatment options

Primary mediastinal large B-cell lymphoma (PMBCL) is a unique B-cell lymphoma variant that arises from a putative thymic medulla B cell. It constitutes 2-4% of non-Hodgkin lymphomas and occurs most frequently in young females. PMBCL is characterized by a diffuse proliferation of medium-to-large B cells associated with sclerosis. Molecular analysis shows that PMBCL is a distinct entity compared to other types of diffuse large B-cell lymphomas. PMBCL is characterized by a locally invasive anterior mediastinal bulky mass. The combination of rituximab with CHOP/CHOP-like regimens followed by mediastinal radiation therapy (RT) is associated with a 5-year progression-free survival of 75-85%. However, the role of consolidation RT still remains uncertain. More intensive regimens, such as DA-EPOCH-R without mediastinal RT, have shown very promising results. The conclusive role of PET-CT scan requires prospective studies and there is hope that this may allow to de-escalate RT and accordingly yield reliable prognostic information.

Primary pulmonary lymphoma in a patient with advanced AIDS

Non-Hodgkin's lymphoma (NHL) is an AIDS defining lesion and risk of NHL most likely correlates with the degree of immunosuppression from HIV. Risk of NHL is highest among patients with CD4 count <50 cells/mL. Primary pulmonary lymphoma (PPL) is an infrequent cause of AIDS-related lymphoma. The authors report a patient with advanced AIDS presenting with recurrent fever and pulmonary nodule seen on the CT scan. The patient remained febrile despite being on broad spectrum antibiotics with no clear source of infection. The patient underwent a bronchoscopy with biopsy of the pulmonary lesion which was most consistent with diffuse large B-cell lymphoma. The patient was started on dose-adjusted etoposide, vincristine, doxorubicin, cyclophosphamide and prednisone (EPOCH) and was noted to be afebrile and a repeat CT scan few weeks later showed resolution of her pulmonary nodule. This case highlights the importance of considering NHL in patients with advanced AIDS presenting with pulmonary nodule and fever.

E-cadherin and CD10 expression in atypical hyperplastic and malignant endometrial lesions

BACKGROUND

Loss of E-cadherin is a critical step for development and progression of malignant tumors. CD10; a marker of non-neoplastic and neoplastic endometrial stroma, is associated with aggressiveness of many epithelial malignancies.

AIMS

To evaluate expression and correlation of E-cadherin and CD10 in endometrial lesions and their possible role in differentiating atypical endometrial hyperplasia from endometrial carcinoma. The association of E-cadherin and CD10 expression with clinico-pathological parameters of endometrial carcinoma was also investigated.

MATERIALS AND METHODS

Fifty four cases including 28 endometrial carcinomas; 19 endometrial hyperplasia and 7 cases of normal endometrial changes were enrolled for this study. The expression of E-cadherin and CD10 was evaluated by immunohistochemistry using the streptavidin-biotin technique.

RESULTS

There was a strong association between malignant change of endometrial glands and membrano-cytoplasmic localization of E-cadherin (p<0.001). Expression of E-cadherin but not CD10 was significantly higher in endometrial carcinomas compared to atypical endometrial hyperplasia (p<0.01). Expression of E-cadherin was not associated with CD10 expression in different endometrial lesions. High grade tumors expressed low levels of both E-cadherin (p<0.01) and CD10 (p<0.05) and serous endometrial carcinoma had low E-cadherin and CD10 expression compared to endometrioid carcinoma (p<0.01 and <0.05, respectively). Expression of both molecules showed no association with depth of tumor invasion or FIGO stage. Tumors with lower E-cadherin or CD10 expression had higher rates of vascular tumor emboli (p<0.01 and <0.07, respectively).

CONCLUSIONS

Although expression of E-cadherin and CD10 in endometrial lesions was not correlated, reduced expression of both molecules could be critical for progression of endometrial carcinoma.

Primary mediastinal large B-cell lymphoma

Primary mediastinal B-cell lymphoma (PMBCL) is a relatively rare lymphoma subtype affecting mainly young adults. Its molecular signature and clinical features resemble classical Hodgkin lymphoma. The optimal chemotherapy for this lymphoma subtype has not been established. The addition of rituximab to anthracycline based chemotherapy improved response rates and survival. Many centers use R-CHOP as standard treatment, but the role of the intensified regimens and consolidation radiotherapy has to be clarified. Recent data coming from retrospective analyses and an ongoing prospective study addressing the problem of consolidation radiotherapy will help to better identify risk groups and apply risk-adapted and effective treatment strategies. The latest research has helped to understand molecular mechanisms of PMBCL pathogenesis and indicated targets of directed therapy for the future.

Prognostic significance of immunophenotypes and a nodular pattern in primary mediastinal large B-cell lymphoma

To investigate the clinicopathological and prognostic significance of a nodular pattern and immunophenotypes in primary mediastinal large B-cell lymphoma (PMBL), histopathological features, including a nodular pattern and immunophenotypes, were analyzed in 58 Japanese PMBL patients. The patients were 23 men and 35 women with a median age of 31 years. The 4-year progression free survival (PFS) rate was 78%, and the 4-year overall survival (OS) rate was 89%. Among the histopathological and immunohistochemical features, Bcl6(+) (P = 0.013), MUM1(+) (P = 0.091), and pale cytoplasm (P = 0.064) were favorable prognostic indicators of PFS, and Bcl6(+) (P = 0.051) and MUM1(+) (P = 0.07) were favorable prognostic indicators of OS. Patients with Bcl2 negativity (n = 11) had 4-year PFS and OS rates of 100%. Histologically, a nodular pattern, resembling nodular sclerosis classical Hodgkin lymphoma (CHL), was observed in 22 patients (38%). However, this was not a significant prognostic indicator. In conclusion, Bcl6(+) , MUM1(+) , Bcl2(-) , and pale cytoplasm are candidate favorable prognostic indicators for PMBL and should be further examined in larger studies. We suggest that PMBL with a nodular pattern may belong to the same histological spectrum as nodular sclerosis CHL.

STAT6-mediated BCL6 repression in primary mediastinal B-cell lymphoma (PMBL)

Primary mediastinal B-cell lymphoma (PMBL) is characterized by aberrant activation of JAK/STAT-signaling resulting in constitutive presence of phosphorylated STAT6 (pSTAT6). In primary PMBL samples pSTAT6 is only expressed in a sub-population of lymphoma cells in a pattern that is reminiscent of that of the BCL6 oncogene. Double-fluorescence staining was carried out to determine the association between these two proteins in ten primary PMBL cases and three available PMBL cell line models. Surprisingly, only a minute fraction of double-positive nuclei was observed, while each sample contained considerable fractions of single-positive pSTAT6 and BCL6 nuclei. The intratumoral coexistence of BCL6+/pSTAT6− and BCL6−/pSTAT6+ subpopulations suggests a negative interaction between these factors. In silico screening of the STAT6 /BCL6 promoters for DNA consensus binding sites identified five STAT-binding-sites in the BCL6 promoter. We confirmed STAT6 binding to the BCL6 promoter in vitro and in vivo by band shift / super shift assays and chromatin immunoprecipitations. Using BCL6 luciferase reporter assays, depletion of STAT6 by siRNA, and ectopic overexpression of a constitutive active STAT6 mutant, we proved that pSTAT6 is sufficient to transcriptionally repress BCL6. Recently developed small molecule inhibitors 79-6 and TG101348 that increases BCL6 target gene expression and decreases pSTAT6 levels, respectively, demonstrate that a combined targeting results in additive efficacy regarding their negative effect on cell viability.

The delineated pSTAT6-mediated molecular repression mechanism links JAK/STAT to BCL6-signaling in PMBL and may carry therapeutic potential.

Knock-down of BCL6 / STAT6 sensitizes primary B cell lymphoma cells for treatment with current therapeutic agents

Primary mediastinal B cell lymphoma (PMBL) is characterized by specific molecular hallmarks including the expression of B Cell Lymphoma factor 6 (BCL6) and the presence of the activated Signal Transducers and Activators of Transcription factor 6 (STAT6). Recently we have shown that combined targeting of BCL6 and activated STAT6 by specific chemical inhibitors in PMBL resulted in additive efficacy regarding their negative effects on cell viability. Given that despite general efficient immuno-chemotherapy in PMBL the delayed treatment-related sequelae remains still a main challenge, we analyzed the role of BCL6 and activated STAT6 in the sensitivity of PMBL cells to the current treatment components. We found that the knock-down of BCL6 / STAT6 by siRNA sensitized the PMBL cells to the effects of R-CHOP components in two of three PMBL cell lines. In one cell line, MedB-1, which is marked by less expression of BCL6 and mutated STAT6, the knock-down of BCL6 / STAT6 did not enhance the efficiency of Doxorubicin, Rituximab, and Vincristin.

Thus, the targeting of BCL6 and STAT6 in addition or prior to the treatment with components of the current immuno-chemotherapy may sensitize the PMBL tumor cells for drug effects, at least in parts of PMBL cases.

Pathobiology of T-cell and NK-cell lymphomas

T-cell and NK-cell lymphomas are uncommon lymphomas with an aggressive clinical course. The causes and precise cellular origins of most T-cell lymphomas are still not well defined. The WHO classification utilizes morphologic and immunophenotypic features in conjunction with clinical aspects and in some instances genetics to delineate a prognostically and therapeutically meaningful categorization. The anatomic localization of neoplastic T-cells and NK-cells parallels in part their proposed normal cellular counterparts and functions. T-cells of the adaptive immune system are mainly based in lymph nodes and peripheral blood, whereas lymphomas derived from T-cells and NK-cells of the innate immune system are mainly extranodal. This approach allows for better understanding of some of the manifestations of the T-cell and NK-cell lymphomas, including their cellular distribution, some aspects of morphology and even associated clinical findings.

Primary mediastinal DLBCL: evolving biologic understanding and therapeutic strategies

Primary mediastinal diffuse large B-cell lymphoma is a quite rare clinicopathologic entity. Molecular analysis shows it to be distinct from other types of diffuse large B-cell lymphoma, and some retrospective analyses suggests that it may respond better to third-generation chemotherapy regimens than to the more commonly used CHOP. The addition of rituximab could reduce these differences; the role of consolidation with local radiotherapy, which is often used to treat residual mediastinal masses, remains. The real role of FDG-PET scanning requires prospective studies, and it is hoped that this may allow the de-escalation of radiation therapy accordingly to yield reliable prognostic information.

The molecular pathogenesis of primary mediastinal large B-cell lymphoma

Primary mediastinal large B-cell lymphoma (PMBCL) is a recognized non-Hodgkin lymphoma entity with unique pathologic, clinical, and molecular characteristics distinct from those of other diffuse large B-cell lymphomas. Immunohistochemical characterization and molecular studies strongly suggest that PMBCL is of germinal center or postgerminal center origin. Pivotal gene expression profiling work defined major deregulated pathway activities that overlap with Hodgkin lymphoma and prompted a more detailed analysis of candidate genes. In particular, the nuclear factor-κB and the Janus Kinase-Signal Transducer and Activator of Transcription signaling pathways are targeted by multiple genomic hits, and constitutive activity of both pathways can be considered molecular hallmark alterations of PMBCL. Moreover, data are emerging giving unique insight into remodeling of the epigenome that affects transcriptional regulation of a multitude of genes. More recently, the tumor microenvironment of PMBCL has shifted into focus based on a number of gene perturbations altering expression of surface molecules that contribute to immune escape. These findings highlight the importance of immune privilege in the pathogenesis of PMBCL and suggest that disrupting crosstalk between the tumor cells and the microenvironment might be a rational new therapeutic target in conjunction with traditional treatment strategies.

Prognostic impact of MUM1 expression by immunohistochemistry on primary mediastinal large B-cell lymphoma

Diffuse large B-cell lymphoma can be classified into two prognostically distinct subgroups with germinal center B-cell-like (CG) and activated B-cell-like (post-CG) characteristics, based on CD10, BCL-6, and MUM1 expression. We performed a retrospective analysis of the clinical variables of 37 patients with primary mediastinal large B-cell lymphoma and the expression of BCL-6 and MUM1 in 22 patients with available tissue. The median age was 30 years, and 70% of the patients were female. BCL-6 and MUM1 were expressed in 64% and 45% of cases, respectively. Five-year overall survival (OS) and disease-free survival (DFS) were 47% and 81%, respectively. In univariate analysis, complete response (p = 0.0001), radiation therapy (p = 0.01), International Prognostic Index (p = 0.001), and MUM1 expression (p = 0.002) correlated with OS. For this group of patients with homogeneous clinical characteristics, response to initial chemotherapy and MUM1 expression were associated with prognosis.

Pathobiology of Primary Mediastinal B-Cell Lymphoma

Controversy still exists over the response to therapy and prognosis of patients with primary mediastinal B-cell lymphoma (PMBL). Recent data from the International Extranodal Lymphoma Study Group (IELSG) suggest that a MACOP-B (methotrexate, adriamycin, cyclophosphamide, vincristine, prednisone, bleomycin) chemotherapy regimen followed by radiotherapy may be a better induction strategy than other previously used treatments. Although the pathobiology of PMBL has been widely studied, its precise histology, phenotype, and molecular characteristics are still not clear. To date, phenotypic analysis has revealed the following phenotype: positivity for CD45 and CD20, but negativity for CD3, CD10, CD21, Class I/II major histocompatibility antigens, and a variety of other immunohistochemical markers. CD79a is generally detected, despite an absence of surface immunoglobulins (Igs). CD30 staining is observed in most cases, but is weaker and less homogeneous than in classic Hodgkin's lymphoma or anaplastic large cell lymphoma. BCL-2 protein is usually expressed but there are few data describing the expression of MUM1/IRF4, PAX5/BSAP, BCL-6, or the B-cell transcription factors BOB.1, Oct-2, and PU.1. Cytogenetic studies reveal gains in segments of chromosome 9p, including amplification of the REL proto-oncogene and the tyrosine kinase gene JAK2. Other molecular findings include: C-myc mutations or rearrangements, p53 mutations, IgV(H), gene mutations, and bcl-2 and mal over-expression. bcl-6 mutations and bcl-2 gene rearrangements are generally absent, suggesting that PMBL is of pre-germinal center (GC) origin. However, two recent reports show isotype-switched Ig genes with a high frequency of somatic hypermutations as well as variants in the 5' noncoding region of the bcl-6 gene. The IELSG collected 137 PMBL cases for extensive pathologic review. Histologically, the lymphomatous growth was predominantly diffuse with sclerosis that induced compartmentalized cell aggregation. It consisted of large cells with varying degrees of nuclear polymorphism and clear to basophilic cytoplasm. Molecular analysis was performed on 40 cases and showed novel findings. More than half of the cases displayed bcl-6 gene mutations, which usually occurred together with functioning somatic IgV(H) gene mutations, and BCL-6 and/or MUM1/IRF4 expression. The present study supports the concept that PBML is derived from activated GC or post-germinal center cells. However, it differs from other aggressive B-cell lymphomas in that it shows defective Ig production despite the expression of Oct-2, BOB.1, and PU.1 transcription factors, and a lack of IgV(H) gene crippling mutations.

[Primary mediastinal large B-cell lymphoma: histopathologic features. A specific tumour]

The diffuse large B-cell lymphomas of the mediastinum were long considered to be a variant of the classic forms of large B-cell lymphomas. However, their clinical and radiological features and especially their histopathological variants point to other lymphoid tumours such as Hodgkin's disease or anaplastic lymphomas, thymic tumours, germ cell tumours or metastatic tumors. The immunohistochemical findings are of prime importance in the diagnosis. This has recently been completed by molecular studies. Currently, they represent a distinct entity among the large B-cell lymphomas, due to their clinical, pathological and molecular features as well as the outcome. The authors report a new case in a young man.

A new immunostain algorithm classifies diffuse large B-cell lymphoma into molecular subtypes with high accuracy

PURPOSE

Hans and coworkers previously developed an immunohistochemical algorithm with approximately 80% concordance with the gene expression profiling (GEP) classification of diffuse large B-cell lymphoma (DLBCL) into the germinal center B-cell-like (GCB) and activated B-cell-like (ABC) subtypes. Since then, new antibodies specific to germinal center B-cells have been developed, which might improve the performance of an immunostain algorithm.

EXPERIMENTAL DESIGN

We studied 84 cases of cyclophosphamide-doxorubicin-vincristine-prednisone (CHOP)-treated DLBCL (47 GCB, 37 ABC) with GCET1, CD10, BCL6, MUM1, FOXP1, BCL2, MTA3, and cyclin D2 immunostains, and compared different combinations of the immunostaining results with the GEP classification. A perturbation analysis was also applied to eliminate the possible effects of interobserver or intraobserver variations. A separate set of 63 DLBCL cases treated with rituximab plus CHOP (37 GCB, 26 ABC) was used to validate the new algorithm.

RESULTS

A new algorithm using GCET1, CD10, BCL6, MUM1, and FOXP1 was derived that closely approximated the GEP classification with 93% concordance. Perturbation analysis indicated that the algorithm was robust within the range of observer variance. The new algorithm predicted 3-year overall survival of the validation set [GCB (87%) versus ABC (44%); P < 0.001], simulating the predictive power of the GEP classification. For a group of seven primary mediastinal large B-cell lymphoma, the new algorithm is a better prognostic classifier (all "GCB") than the Hans' algorithm (two GCB, five non-GCB).

CONCLUSION

Our new algorithm is significantly more accurate than the Hans' algorithm and will facilitate risk stratification of DLBCL patients and future DLBCL research using archival materials.

Commentary on the WHO classification of tumors of lymphoid tissues (2008): "Gray zone" lymphomas overlapping with Burkitt lymphoma or classical Hodgkin lymphoma

The 2008 WHO Classification of Tumors of Haematopoietic and Lymphoid Tissues has introduced two new categories of high-grade B-cell lymphomas: entities in which features of diffuse large B-cell lymphoma (DLBCL) overlap with Burkitt lymphoma (DLBCL/BL) or classical Hodgkin lymphoma (DLBCL/HL). The DLBCL/BL category encompasses cases that resemble Burkitt lymphoma morphologically, but have one or more immunophenotypic or molecular genetic deviations that would exclude it from the BL category; conversely, some cases have immunophenotypic and/or genetic features of BL, but display cytologic variability unacceptable for BL. Many of the cases in the DLBCL/BL category contain a translocation of MYC as well as either BCL2 or BCL6 (so-called double-hit lymphomas) and have a very aggressive clinical behavior. The DLBCL/HL category encompasses lymphomas that exhibit the morphology of classical Hodgkin lymphoma but the immunophenotype of DLBCL, or vice versa. Most DLBCL/HL cases described present as mediastinal masses, but this category is not limited to mediastinal lymphomas. These new categories acknowledge the increasing recognition of cases that display mixed features of two well-established diseases. Whether the existence of such cases reflects shortcomings of our current diagnostic armamentarium or a true disease continuum in which such hybrid or intermediate neoplasms actually exist remains to be determined.

Primary mediastinal B-cell lymphoma: treatment and therapeutic targets

Primary mediastinal B-cell lymphoma (PMBCL) is a recognised subtype of diffuse large B-cell lymphoma according to the WHO classification that represents approximately 5% of aggressive lymphomas, and 2% of all cases of lymphomas. It presents with unique clinical, morphologic and immunophenotypic characteristics that define the disease. Retrospective studies have found that PMBCL patients have excellent survival rates with a distinct plateau and a trend to better outcome if treated with dose-intensified chemotherapy with MACOPB or VACOPB. In spite of the multiple molecular data known, generated on the pathogenesis of this tumour, treatment is still essentially based on a combination of chemo and immunotherapy. We take this opportunity for reviewing the recent biologic data provided by gene expression profiling of the tumour, for discussing new potential therapeutic targets.

Extranodal lymphoma

Lymphomas arising in extranodal sites are intriguing. The types of lymphomas encountered vary widely from one extranodal site to another. For many types of extranodal lymphomas, there are distinctive clinicopathologic features, sometimes including association with an underlying immunodeficiency syndrome, autoimmune disease, infection, or other immunologic disorder, or a predilection to affect patients of certain ethnic origins. Presented below is a review of lymphomas that are encountered most often in extranodal sites.

Das mediastinale (thymische) großzellige B-Zell-Lymphom

Mediastinal B-cell lymphoma is a locally highly aggressive tumour which was first described in the early 1980s. The incidence is about 2-3% of all non-Hodgkin's lymphomas. The conceptional evolution of this lymphoma entity was hampered by its low incidence and the broad spectrum of morphological variants present. However, since mediastinal B-cell lymphoma has distinct morphological, immunological, genetic, and clinical features, it has been listed in the revised European-American Classification of Lymphoid Neoplasms (REAL-Classification) since 1994 as a variant of diffuse large B-cell lymphoma. In the World Health Organization classification of malignant lymphomas, mediastinal B-cell lymphoma is now listed with an own disease code (ICD-9679/3).

Primary Mediastinal Large B-Cell Lymphoma: A Single-Center Study of Clinicopathologic Characteristics

Primary mediastinal large B-cell lymphoma (PMLBCL) is a subset of LBCL with unique clinicopathologic features. Some studies have raised the question of differences in biological features and clinical course among patients from different parts of the world. We conducted a retrospective clinicopathologic analysis of 24 patients with PMLBCL from a single center in Croatia. We also conducted the first investigation of the frequency of lymphotropic viruses human herpesvirus 6 (HHV-6) and HHV-8 in lymphoid lesions of this disease. The clinical characteristics of the patients were as expected, with high International Prognostic Index scores, elevated serum lactate dehydrogenase (LDH) levels, and bulky disease being adverse prognostic factors. Only 6 patients (25%) showed CD30 expression, and Bcl-6 protein expression was, in our series, prognostically favorable (P = .0401). One patient's tumor had detectable HHV-6 genome sequence, but no HHV-8 sequences were detected in any tumors. Two thirds of the patients received CHOP chemotherapy (cyclophosphamide, hydroxydaunomycin, vincristine, and prednisone) with a relatively low complete remission rate (43.8%; median follow-up, 33.8 months). This study confirmed the moderate preponderance among PMLBCL patients of young females with B symptoms and elevated LDH levels. The CHOP regimen proved effective as first-line therapy only in patients with limited disease. Therefore, other third-generation chemotherapy protocols may be considered for treatment, especially in patients with bulky and advanced disease.

Targeted somatic mutation of the BCL6 proto-oncogene and its impact on lymphomagenesis

Cloning translocation breakpoints which cluster suspiciously to specific chromosomal loci has proved fruitful, leading to the identification of genes implicated in the onset of hematological malignancy. One of the most notable is BCL6, located on chromosome 3q27. The BCL6 is now known to encode a nuclear transcriptional repressor, with pivotal roles in germinal center (GC) formation and regulation of lymphocyte function, differentiation and survival. Unusually, the BCL6 gene locus is also actively targeted by the somatic mutation (SM) mechanism, at a rate indicative of specific, regulated events in both normal and malignant B-cells. These mutations occur in approximately 30% of normal centrocytes and centroblasts, but not in naive or pre-GC B-cells. They are also observed in approximately 70% of diffuse large B-cells lymphomas, approximately 30% of follicular lymphomas (FL) and at various frequencies in many lymphoma subtypes. Mutations are generated in the 5' proximity of the BCL6 promoter, including the first intron and are mainly single nucleotide substitutions, but with insertions and deletions also observed. Mutations in BCL6 occur independently of translocations, although mutational levels can be dramatically influenced by aberrantly translocated chromosomal elements, which map in the vicinity of the gene. Indeed, SMs are directly implicated in the generation of chromosomal translocations, as suggested by the overlap of the breakpoint cluster region and the mutational cluster domain. The prognostic value of the overall level of BCL6 mutations in specific lymphoma populations is, in the main, not as yet fully resolved. The accumulation of mutations in BCL6 during high grade transformation of FL, a mutational clustering and specific recurrent mutations suggest that some mutations may be selected for by their effect on the survival of the tumoral clone. In fact, it is now clear that SM can target and disrupt regulatory motifs in BCL6 to result in upregulated gene expression. Exogenous factors can also perturbate SM in BCL6. Viral infection elevates BCL6 mutational activity, suggesting a potential link with onset of virus-associated lymphoma. These findings to date reveal several mechanisms which can influence specific mutations targeting BCL6, and which may contribute to lymphomagenesis by dysregulating control of BCL6 expression.

CD23 expression in mediastinal large B-cell lymphomas

AIMS

Mediastinal large B-cell lymphoma (MLBCL) is a subtype of diffuse large B-cell lymphoma (DLBCL) in the WHO classification with peculiar features, such as female prevalence, young patient age and bulky presentation. It shows a B-cell phenotype with variable expression of surface immunoglobulin, negative CD21 and CD10 and positive CD30 in a large number of cases. An origin from activated thymic B cells has been suggested in several studies. A subpopulation of large, dendritic cells (asteroid cells) strongly expressing CD23 has been identified amongst thymic B cells and these could represent the normal cellular counterpart for this type of primary mediastinal large cell lymphoma.

METHODS AND RESULTS

To explore this possibility, we immunostained 24 cases of primary mediastinal lymphomas and 100 cases of non-mediastinal, nodal and extranodal, DLBCLs for CD23 in routinely processed paraffin-embedded tissues.

CONCLUSIONS

Our results show that a vast majority (70%) of mediastinal lymphomas strongly express CD23 whilst the same antigen is expressed in only 15% of non-mediastinal nodal DLBCLs and 9% of non-mediastinal extranodal DLBCLs. These results support the hypothesis that most cases of MLBCL arise from activated dendritic thymic B cells. We also suggest that CD23 should be included in the panel of antibodies currently used to characterize this subtype of DLBCL.

Point mutation of 5’ noncoding region of BCL-6 gene in primary gastric lymphomas

AIM: To investigate the mutations of the 5’ noncoding region of BCL-6 gene in Chinese patients with primary gastric lymphomas.

METHODS: PCR and direct DNA sequencing were used to identify BCL-6 gene mutations in the 5’ noncoding region in 29 cases of gastric diffuse large B-cell lymphoma (DLBCL) and 18 cases of gastric mucosa-associated lymphoid tissue (MALT) lymphoma as well as 10 cases of reactive hyperplasia of lymph node (LRH).

RESULTS: Six of 29 gastric DLBCLs (20.7%), 4 of 18 gastric MALT lymphomas (22.2%) and 1 of 10 LRHs(10%) were found to have mutations. All mutations were single-base substitutions and the frequency of single-base changes was 0.20×10^-2 -1.02×10^-2 per bp.

CONCLUSION: Point mutations in the 5’ noncoding region of BCL-6 gene are found in Chinese patients with primary gastric DLBCLs and MALT lymphomas, suggesting that they may, in some extent, participate in the pathogenesis of primary gastric DLBCLs and MALT lymphomas.

Applications of Flow Cytometry and Immunohistochemistry to Diagnostic Hematopathology

Objective.—Diagnostic hematopathology depends on the applications of flow cytometric immunophenotyping and immunohistochemical immunophenotyping combined with the cytomorphology and histologic features of each case. Select cases may require additional ancillary cytogenetic and molecular studies for diagnosis. The purpose of this review is to focus on the applications of flow cytometric and immunohistochemical immunophenotyping of paraffin-embedded tissue to diagnostic hematopathology. Advantages and disadvantages of these techniques are examined.

Data Sources.—The literature is extensively reviewed (PubMed 1985–2003) with an emphasis on the most recent applications and those that are most useful clinically, both diagnostically and prognostically.

Study Selection.—Studies were selected based on statistically significant results in large studies with reported adequate clinical follow-up.

Data Extraction.—The methodology was reviewed in the selected studies to ensure reliable comparison of reported data.

Data Synthesis.—Flow cytometric immunophenotyping offers the sensitive detection of antigens for which antibodies may not be available for paraffin immunohistochemical immunophenotyping. However, paraffin immunohistochemical immunophenotyping offers preservation of architecture and evaluation of expression of some proteins, which may not be available by flow cytometric immunophenotyping. These techniques should be used as complimentary tools in diagnostic hematopathology.

Conclusions.—There are extensive applications of flow cytometric and immunohistochemical immunophenotyping to diagnostic hematopathology. As cytogenetic and molecular findings evolve in diagnostic hematopathology, there may be additional applications of flow cytometric and immunohistochemical immunophenotyping to this field of pathology.

Variability in immunophenotype in diffuse large B-cell lymphoma and its clinical relevance

Diffuse large B-cell lymphoma (DLBCL), the single largest category of lymphoma, is a clinically and biologically heterogeneous disease entity. Clinically, patients differ in their mode of presentation and respond variably to therapy. A combination of clinical parameters can be used to predict the patient's response to therapy and survival. The pathological variability of DLBCL is expressed in morphology, immunophenotype, cytogenetic and molecular genetic features. Numerous markers detectable by immunohistochemistry and linked to different aspects of tumour biology have been studied in DLBCL, including lineage-associated and immune markers, proliferation and apoptosis markers, cell adhesion molecules, and more recently stage-specific markers of B-cell differentiation. This review summarizes these studies in regard to their clinical significance and in the light of recent advances in our understanding of the molecular pathology and histogenesis of DLBCL.

Critical evaluation of Bcl-6 protein expression in diffuse large B-cell lymphoma of the stomach and small intestine

Diffuse large B-cell lymphoma (DLBCL) of the gastrointestinal tract is heterogeneous, including mucosa-associated lymphoid tissue (MALT) origin and non-MALT, and they are indistinguishable. MALT lymphoma is a tumor of a post-germinal center (GC) memory B-cell origin, which is negative for Bcl-6 protein expression in low-grade but may become positive in high-grade tumors. Because Bcl-6 expression patterns in lymphoma of GC and non-GC B-cell origins have recently been characterized and CD10 is generally regarded as a specific marker for GC B cells, we critically evaluated gastric and small intestinal DLBCLs to see whether it is possible to identify tumor of GC B-cell origin by immunostaining in archival specimens. High-grade MALT lymphoma (H-ML) of the stomach (n = 20) was defined by the presence of a concomitant lymphoepithelial lesion and/or follicular colonization; and DLBCLs de novo, both gastric (n = 31) and intestinal (n = 21), were defined by the absence of the above features. Immunostaining for Bcl-6 and CD10 was done using formalin-fixed, paraffin-embedded sections and was examined independently by three pathologists. Staining for Bcl-6 was positive (>10% of tumor cells) in 55 of 72 cases. However, two distinct patterns were recognized among those positive: diffusely dense (>75%) and sporadic (<75%). The former was further characterized by a consistency of Bcl-6+ tumor cell density at any given area, resembling the staining pattern of the GC or follicular lymphoma (FL) (GC/FL pattern), whereas the latter was, besides less dense population, by variable density from area to area. The GC/FL pattern was observed in 36% and 38% of gastric and intestinal DLBCLs de novo, respectively, but in none of the gastric H-ML. CD10 was positive in 12 of 71 cases (17%), all coexpressing Bcl-6. CD10+ tumors were more frequent in the intestinal (33%) than in gastric DLBCLs ( approximately 15%). Significantly, CD10 expression was observed in three gastric H-MLs, including one that displayed a distinct lymphoepithelial lesion.

IN CONCLUSION

1). tumors showing a diffusely dense pattern of Bcl-6 expression should be distinguished from those showing a sporadic pattern; for the former most likely represents the tumor of GC B-cell derivation, and the latter non-GC, including MALT lymphoma; 2). tumor of GC B-cell origin thus defined accounted for about one third of gastric as well as intestinal DLBCLs de novo but none of the gastric H-ML; and 3). CD10 expression can be seen in MALT lymphomas and should not be used as the marker for GC B cells.

Detection of germinal center B-cell lymphoma in archival specimens: critical evaluation of Bcl-6 protein expression in diffuse large B-cell lymphoma of the tonsil

Expression of Bcl-6 and CD10, markers for the tumor of the germinal center (GC) B-cell derivation, has been studied in primary diffuse large B-cell lymphomas (DLBCLs) of the lymph node, gastrointestinal tract, and mediastinum. In these studies, the coexpression rate of CD10 and Bcl-6 was relatively constant at 30% approximately 40%, but the frequency of Bcl-6+ tumors varied from 55% to 100%, raising doubts about the usefulness of Bcl-6 expression in identifying the tumor of GC B-cell derivation. Because the expression of Bcl-6 in tumors of non-GC B-cell origin has recently been reported, we critically evaluated the expression of Bcl-6 and CD10 in primary DLBCLs of the tonsil, a relatively common tumor in Japan and Korea. The cases (n = 51) represented a consecutive series for any recent 2-year period at several teaching hospitals in Korea and Japan. Formalin-fixed, paraffin-embedded specimens were used for immunostaining. Staining for Bcl-6 and CD10 was positive in 44 (86%) and 22 cases (45%), respectively. However, among those positive for Bcl-6 (>10% Bcl-6+ tumor cells), 2 basic patterns were recognized: uniform and nonuniform. The uniform pattern was characterized by a dense population (>75%) and a consistent density in any given area, resembling the staining pattern observed in GC or follicular lymphoma (FL) (the "GC/FL" pattern). In contrast, the nonuniform pattern exhibited a varying density from area to area, as well as a less-dense population (<75%). The uniform pattern was observed in 26 cases (51%). All but 1 (95%) of the CD10+ tumors coexpressed Bcl-6, with most (82%) displaying the uniform pattern. We conclude that tumors showing a uniform pattern of Bcl-6 expression should be distinguished from those showing a nonuniform pattern, because the former most likely represent tumors of GC B-cell derivation and the latter most likely represent tumors of non-GC derivation. GC B-cell lymphoma thus defined accounted for 51% of tonsillar DLBCL, a proportion comparable to that of the nodal DLBCL. CD10 expression correlated with the "GC/FL" pattern, but appeared to be not essential for the identification of GC B-cell lymphoma. This study suggests that a significant proportion of tonsillar DLBCLs in Asia is of GC B-cell origin rather than of mucosa-associated lymphoid tissue origin. This finding may have significance for clinical management of these lymphomas.

Interleukin 4-induced gene 1 is activated in primary mediastinal large B-cell lymphoma

The molecular markers that distinguish primary mediastinal large B-cell lymphoma (PMBL) from nonmediastinal diffuse large B-cell lymphomas (NM-DLBLs) remain to be identified. Using cDNA representational difference analysis to compare PMBL and NM-DLBL transcripts, we isolated a cDNA fragment homologous to the mouse B-cell interleukin 4 (IL-4)-inducible gene FIG1 (interleukin 4-induced gene 1) transcript. The human FIG1 mRNA encodes a 567 amino acid protein that comprises a signal peptide and a large flavin-binding amino oxidase domain, and shares significant homology with secreted apoptosis-inducing L-amino acid oxidases. Northern blot studies showed that FIG1 mRNA expression is mainly restricted to lymphoid tissues. It is expressed at low levels in thymus, spleen, tonsils, and reactive lymph nodes, and is highly up-regulated in IL-4+CD40-activated tonsillar B cells. Interestingly, in human B-cell lines, FIG1 mRNA expression appeared restricted to the PMBL-derived MedB-1 and Karpas 1106 cell lines. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), we demonstrated that all but one PMBL (16/17) displayed high FIG1 mRNA levels, whereas most NM-DLBLs (12/18) and all low-grade B-cell lymphomas tested (8/8) exhibited low FIG1 mRNA levels. The difference between PMBLs and NM-DLBLs was statistically significant (Fisher test; P =.0003). Southern blot studies did not show rearrangement of the FIG1 gene. FIG1 gene expression might be due to a constitutive activation of a cytokine signaling pathway in PMBL.

Primary and secondary cutaneous diffuse large B-cell lymphomas: a multiparameter analysis of 25 cases including fluorescence in situ hybridization for t(14;18) translocation

Although primary cutaneous diffuse large B-cell lymphomas (DLBCLs) except for those of the leg are grouped together with primary cutaneous follicle center cell lymphoma in the European Organization for Research and Treatment of Cancer classification of primary cutaneous lymphomas, they typically lack the usual phenotypic profile of follicular lymphoma. Whether they are truly of follicular center cell origin, have a molecular pathogenesis similar to nodal follicular lymphoma, or have any biologic features that distinguish them from secondary DLBCL involving skin remains uncertain. To address these issues, a retrospective multiparameter study of 25 patients including clinical, histologic, immunophenotypic, and cytogenetic analyses was performed. A classic CD10+, bcl-6+ follicular center cell profile was found in 10 (40%) cutaneous DLBCL (2 of 11 primary, 5 of 8 secondary, 3 of 6 unclassified) with bcl-2 expression seen only in the nonprimary cases. Of the remaining cases, 14 cases (56%) were CD10-, bcl-6+, bcl-2+/- (9 primary) and one case (4%) was CD10-, bcl-6-, bcl-2+ (0 primary). Fluorescence in situ hybridization analysis showed a t(14;18) in 0 of 9 primary and 3 of 5 secondary cases. Primary cases were frequently found in the head/neck region, whereas secondary cases were more common on the trunk and extremities. Patients with primary disease were all alive, usually having received only local therapy, at a median follow-up of 19 months. Most secondary cases were treated with chemotherapy with only one untreated patient dead of disease at a median follow-up of 5 months. Primary cutaneous DLBCLs therefore appear to be distinctive as they have fewer features of follicular lymphoma than do secondary cases. Nevertheless, some appear to be of follicular center cell origin, even though they probably have a different molecular pathogenesis than most nodal follicular lymphomas.

Primary mediastinal B-cell lymphoma: high frequency of BCL-6 mutations and consistent expression of the transcription factors OCT-2, BOB.1, and PU.1 in the absence of immunoglobulins

Although primary mediastinal (thymic) large B-cell lymphoma has been primarily studied, its precise phenotype, molecular characteristics, and histogenesis are still a matter of debate. The International Extranodal Lymphoma Study Group collected 137 such cases for extensive pathological review. Histologically, the lymphomatous growth was predominantly diffuse with fibrosis that induced compartmentalized cell aggregation. It consisted of large cells with varying degrees of nuclear polymorphism and clear to basophilic cytoplasm. On immunohistochemistry, the following phenotype was observed: CD45(+), CD20(+), CD79a(+), PAX5/BSAP(+), BOB.1(+), Oct-2(+), PU.1(+), Bcl-2(+), CD30(+), HLA-DR(+), MAL protein(+/-), Bcl-6(+/-), MUM1/IRF4(+/-), CD10(-/+), CD21(-), CD15(-), CD138(-), CD68(-), and CD3(-). Immunoglobulins were negative both at immunohistochemistry and in situ hybridization. Molecular analysis, performed in 45 cases, showed novel findings. More than half of the cases displayed BCL-6 gene mutations, which usually occurred along with functioning somatic IgV(H) gene mutations and Bcl-6 and/or MUM1/IRF4 expression. The present study supports the concept that a sizable fraction of cases of this lymphoma are from activated germinal center or postgerminal center cells. However, it differs from other aggressive B-cell lymphomas in that it shows defective immunoglobulin production despite the expression of OCT-2, BOB.1, and PU.1 transcription factors and the lack of IgV(H) gene crippling mutations.

Diffuse large B-cell lymphoma: one or more entities? Present controversies and possible tools for its subclassification

Diffuse large B-cell lymphoma (DLBCL) is the commonest type of lymphoid tumour world-wide. This category was included both in the REAL and WHO Classification aiming to lump together all malignant lymphomas characterized by the large size of the neoplastic cells, B-cell derivation, aggressive clinical presentation, and the need for highly effective chemotherapy regimens. These tumours are detected as primary or secondary forms both at the nodal and extranodal levels, in immunocompetent hosts as well as in patients with different types of immunosuppression. They display a significant variability in terms of cell morphology and clinical findings, which justifies the identification of variants and subtypes. Among the latter, the primary mediastinal one does actually correspond to a distinct clinicopathological entity. Immunophenotypic, tissue microarray and molecular studies underline the extreme heterogeneity of DLBCLs and suggest a subclassification of the tumour, based on the identification of different pathogenic pathways, which might have much greater relevance than pure morphology for precise prognostic previsions and adoption of ad hoc therapies. The more recent acquisitions on the pathobiology of DLBCLs are reviewed in the light of the authors' experience, aiming to contribute to the existing debate on the topic.