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After 8 years, the WHO has now published the updated version of the 4th edition of the classification of hematopoietic and lymphoid tumors. This update provides a conceptual rewrite of existing entities as well as some new provisional entities and categories, particularly among the aggressive B‑cell lymphomas. Important new diagnostic categories include the high-grade B‑cell lymphomas, the large B‑cell lymphoma with IRF4 rearrangement, and the Burkitt-like lymphoma with 11q aberrations. Of particular importance, new concepts concerning the taxonomy and classification of early lymphoid lesions or precursor lesions are included, such as the in situ follicular neoplasia or the in situ mantle cell neoplasia. In addition, the concept of indolent lymphoproliferations, such as breast-implant-associated anaplastic large cell lymphoma and the indolent T‑cell lymphoproliferative disorder of the gastrointestinal tract, has been strengthened. Finally, diagnostic criteria for existing lymphoma entities have been refined.

A revision of the nearly 8-year-old World Health Organization classification of the lymphoid neoplasms and the accompanying monograph is being published. It reflects a consensus among hematopathologists, geneticists, and clinicians regarding both updates to current entities as well as the addition of a limited number of new provisional entities. The revision clarifies the diagnosis and management of lesions at the very early stages of lymphomagenesis, refines the diagnostic criteria for some entities, details the expanding genetic/molecular landscape of numerous lymphoid neoplasms and their clinical correlates, and refers to investigations leading to more targeted therapeutic strategies. The major changes are reviewed with an emphasis on the most important advances in our understanding that impact our diagnostic approach, clinical expectations, and therapeutic strategies for the lymphoid neoplasms.

Aims: To study the expression of CD2-associated protein (CD2AP), an adaptor protein involved in T-cell signalling and renal function, in normal, reactive and neoplastic human lymphoid tissues., Methods and Results: We used immunohistochemical techniques to evaluate monoclonal antibodies against CD2AP on over 400 formalin fixed paraffin embedded tissue blocks retrieved from the host institutions of three authors. The samples tested included normal, reactive and neoplastic lymphoid tissue. In lymphoid tissues, strong CD2AP staining was observed in plasmacytoid dendritic cells (pDCs), weak and variable in mantle zone B cells and moderate in rare germinal center cells. CD2AP labeled cortical and rare medullary thymocytes and isolated mononuclear cells in bone marrow trephines. Furthermore, epithelial and endothelial cells expressed CD2AP. Among neoplasms, the greatest number of CD2AP-positive cases were found in diffuse large B cell (21/94), NK T-cell lymphomas (7/67), "blastic plasmacytoid dendritic cell neoplasms" (9/10) and some types of solid tumor., Conclusions: Our finding that mature peripheral T cells are CD2AP-negative but immature cortical thymocytes are positive may prove useful for diagnostic purposes. Moreover, our results demonstrate that CD2AP represents a useful marker of normal and neoplastic pDC and may be used in a diagnostic panel in reactive or neoplastic lymphoid proliferations.

The World Health Organization classification of lymphoid neoplasms updated in 2008 represents a worldwide consensus on the diagnosis of these tumors and is based on the recognition of distinct diseases, using a multidisciplinary approach. The updated classification refined the definitions of well-recognized diseases, identified new entities and variants, and incorporated emerging concepts in the understanding of lymphoid neoplasms. However, some questions were unresolved, such as the extent to which specific genetic or molecular alterations define certain tumors, and the status of provisional entities, categories for which the World Health Organization working groups felt there was insufficient evidence to recognize as distinct diseases at this time. In addition, since its publication, new findings and ideas have been generated. This review summarizes the scientific rationale for the classification, emphasizing changes that have had an effect on practice guidelines. The authors address the criteria and significance of early or precursor lesions and the identification of certain lymphoid neoplasms largely associated with particular age groups, such as children and the elderly. The issue of borderline categories having overlapping features with large B-cell lymphomas, as well as several provisional entities, is reviewed. These new observations chart a course for future research in the field.

Inappropriate activation of the NOTCH signaling pathway, for example, by activating mutations, contributes to the pathogenesis of various human malignancies. Here, we demonstrate that aberrant expression of an essential NOTCH coactivator of the Mastermind-like (MAML) family provides an alternative mechanism to activate NOTCH signaling in human lymphoma cells. We detected high-level MAML2 expression in several B cell-derived lymphoma types, including classical Hodgkin lymphoma (cHL) cells, relative to normal B cells. Inhibition of MAML-protein activity by a dominant negative form of MAML or by small hairpin RNAs targeting MAML2 in cHL cells resulted in downregulation of the NOTCH target genes HES7 and HEY1, which we identified as overexpressed in cHL cells, and in reduced proliferation. Furthermore, a NOTCH gene-expression signature in cHL cells confirmed their cell-autonomous NOTCH activity. Finally, in line with the essential role of MAML proteins for assembly and activity of the NOTCH transcriptional complex (NTC), we show that MAML-derived small-peptide constructs block NOTCH activity and disrupt NTC formation in vitro. These data strongly suggest direct targeting of the NTC as treatment strategy for NOTCH-dependent malignancies.

Mammalian genomes contain many repetitive elements, including long terminal repeats (LTRs), which have long been suspected to have a role in tumorigenesis. Here we present evidence that aberrant LTR activation contributes to lineage-inappropriate gene expression in transformed human cells and that such gene expression is central for tumor cell survival. We show that B cell-derived Hodgkin's lymphoma cells depend on the activity of the non-B, myeloid-specific proto-oncogene colony-stimulating factor 1 receptor (CSF1R). In these cells, CSF1R transcription initiates at an aberrantly activated endogenous LTR of the MaLR family (THE1B). Derepression of the THE1 subfamily of MaLR LTRs is widespread in the genome of Hodgkin's lymphoma cells and is associated with impaired epigenetic control due to loss of expression of the corepressor CBFA2T3. Furthermore, we detect LTR-driven CSF1R transcripts in anaplastic large cell lymphoma, in which CSF1R is known to be expressed aberrantly. We conclude that LTR derepression is involved in the pathogenesis of human lymphomas, a finding that might have diagnostic, prognostic and therapeutic implications.

Activated RAS/BRAF oncogenes induce cellular senescence as a tumor-suppressive barrier in early cancer development, at least in part, via an oncogene-evoked DNA damage response (DDR). In contrast, Myc activation-although producing a DDR as well-is known to primarily elicit an apoptotic countermeasure. Using the Emu-myc transgenic mouse lymphoma model, we show here in vivo that apoptotic lymphoma cells activate macrophages to secrete transforming growth factor beta (TGF-beta) as a critical non-cell-autonomous inducer of cellular senescence. Accordingly, neutralization of TGF-beta action, like genetic inactivation of the senescence-related histone methyltransferase Suv39h1, significantly accelerates Myc-driven tumor development via cancellation of cellular senescence. These findings, recapitulated in human aggressive B cell lymphomas, demonstrate that tumor-prompted stroma-derived signals may limit tumorigenesis by feedback senescence induction., (Copyright 2010 Elsevier Inc. All rights reserved.)

The recent World Health Organization (WHO) classification of hematopoietic and lymphoid tissue tumors represents the first worldwide consensus classification of these malignancies. However, the applicability of this classification to a representative number of hepatic lymphomas in liver biopsy specimens has not yet been investigated. The frequency and infiltration pattern of a series of 205 liver biopsies with lymphoma manifestations was analyzed with the aid of immunohistochemical and molecular pathological analyses. Diffuse large B-cell lymphoma (DLBCL) was by far the most frequent entity, comprising 45% of the cases analyzed. Using a previously published immunohistochemical algorithm, 35% of 80 DLBCL were assigned to a germinal center B-cell-like (GCB) and 65% to a non-GCB group. Most B-cell lymphoma entities involving the liver revealed a characteristic infiltration pattern. Diagnostically challenging entities were T-cell-rich B-cell lymphomas, anaplastic large cell lymphomas and peripheral T-cell lymphomas, which frequently required additional molecular clonality assessment. Overall, the percentage of T-cell lymphomas in the liver (12%) was higher as compared to other extranodal sites except for the skin and the small intestine. This study provides relevant data on the distribution of hepatic lymphomas and demonstrates the applicability of the WHO classification proposing a diagnostic algorithm for liver biopsies.

The classification of malignant lymphomas according to the WHO scheme of 2001 is based on modern knowledge of B- and T-cell differentiation, the immunophenotype and genetic alterations of the neoplastic cells, as well as on clinical features. Conventional histology does not suffice for a reliable diagnosis of lymphoma diseases and the application of additional methods is required. Immunophenotyping by means of immunohistochemistry is indicated in practically all instances. In a number of cases, the analysis of clonality by PCR and cytogenetic alterations by FISH also need to be applied. A high risk cause of B-cell lymphomagenesis involves rearrangements at the immunoglobulin locus and events occurring during the germinal centre reaction (somatic mutations and immunoglobulin heavy chain class switch) which may result in molecular accidents in the form of chromosomal translocations and/or gain or loss of functional mutations. This may disrupt B-cell homeostasis resulting in increased proliferation, inhibition of apoptosis or both. Clinical behaviour may be influenced by the microenvironment, e.g. T-cells, cytokines and pathogenic microorganisms.

Transcription factors play a crucial role during hematopoiesis by orchestrating lineage commitment and determining cellular fate. Although tight regulation of transcription factor expression appears to be essential, little is known about the epigenetic mechanisms involved in transcription factor gene regulation. We have analyzed DNA methylation profiles of 13 key transcription factor genes in primary cells of the hematopoietic cascade, lymphoma cell lines and lymph node biopsies of diffuse large B-cell- and T-cell-non-Hodgkin lymphoma patients. Several of the transcription factor genes (SPI1, GATA3, TCF-7, Etv5, c-maf and TBX21) are differentially methylated in specific cell lineages and stages of the hematopoietic cascade. For some genes, such as SPI1, Etv5 and Eomes, we found an inverse correlation between the methylation of the 5' untranslated region and expression of the associated gene suggesting that these genes are regulated by DNA methylation. Differential methylation is not limited to cells of the healthy hematopoietic cascade, as we observed aberrant methylation of c-maf, TCF7, Eomes and SPI1 in diffuse large B-cell lymphomas. Our results suggest that epigenetic remodelling of transcription factor genes is a frequent mechanism during hematopoietic development. Aberrant methylation of transcription factor genes is frequently observed in diffuse large B-cell lymphomas and might have a functional role during tumorigenesis.

The simultaneous manifestation of different lymphomas in the same patient or even in the same tissue, defined as composite lymphoma, is very rare. The exceptional case of a patient who, presented with simultaneous manifestation of three different lymphomas after 30 years of successful treatment of a nodal T cell lymphoma is reported here. The three lymphomas were: (1) primary cutaneous marginal zone B cell lymphoma (MZBL); (2) nodal Epstein-Barr virus (EBV)-associated classic Hodgkin's lymphoma (cHL) of the B cell type; and (3) peripheral T cell lymphoma coexisting in the skin and cervical lymph node. Immunohistochemical and molecular analyses showed different clonal origins of EBV-negative cutaneous MZBL and EBV-positive B cell cHL and, in addition, the presence of the same clonal T cell population in the skin and lymph node. The simultaneous occurrence of three different, clonally unrelated lymphomas in one patient at the same time has not been reported yet.

Primary hepatic lymphomas represent rare neoplasms, which are partly observed in association with chronic viral hepatitis, immunosuppression and autoimmune diseases. In contrast, secondary hepatic lymphomas are much more frequent and represent disseminated disease. Lymphomas involving the liver include, with decreasing frequency, diffuse large B-cell lymphoma, small lymphocytic lymphoma, Hodgkin's lymphoma, peripheral T-cell lymphoma, follicular lymphoma and extranodal marginal zone B-cell lymphoma. Many B-cell lymphomas in the liver reveal a characteristic infiltration pattern allowing a rapid and cost-effective diagnosis based on focused immunohistochemical analyses. In contrast, most T-cell lymphomas show a more diverse morphology, which is sometimes difficult to differentiate from a reactive condition. Therefore, additional molecular analyses are frequently necessary. The differential diagnosis includes hepatitis and inflammatory bile duct diseases, undifferentiated carcinoma, inflammatory myofibroblastic tumor as well as histiocytic and dendritic cell neoplasms.

Background: The prognosis of intraocular lymphoma (IOL) is poor, and the optimal treatment has yet to be defined. This study assesses the clinical characteristics and outcome of patients with IOL diagnosed and treated in the new millennium., Methods: Patient data in this retrospective multicentre study were compiled by standardised questionnaires sent to seven university ophthalmology departments. All cases diagnosed with primary and secondary IOL in the past 5 years not associated with HIV infection were included., Results: Twenty-two patients, 11 men and women; median age 64 (range 38-83) years, median Karnofsky performance status 90% (range 50-100%), were included. Nineteen patients had primary IOL (PIOL): 13 a newly diagnosed disease and six an ocular relapse of primary central nervous system lymphoma (PCNSL). Three patients had secondary IOL. First-line treatment for IOL included systemic chemotherapy in 13 cases, ocular radiation in six and intraocular chemotherapy in three. Complete remission was achieved in 14/20 evaluable patients, partial remission in five and stable disease in one. All patients treated with ifosfamide (IFO) or trofosfamide (TRO) (n=8) responded. Median progression-free survival (PFS) and overall survival were 10 (range 1+ to 44.5+) and 22.5 (range 1+ to 49+) months, respectively. Patients with newly diagnosed PIOL and ocular relapse of PCNSL had a median PFS of 10 (range 1+ to 44.5+) and 6 (range 2 to 6+) months, respectively. Median PFS was 12 (range 3+ to 22.5+) months after systemic and 5.5 (range 1+ to 44.5+) months after local first-line therapy., Conclusions: The prognosis of PIOL is similar to that of PCNSL without ocular involvement. Systemic therapy possibly prolongs PFS as compared with local management of (P)IOL. The high response rate to monotherapy with IFO and TRO is promising.

Objective: The aim of this study was to characterize the clinical presentation, course, and outcome of low-grade primary central nervous system lymphoma., Methods: Cases were assessed in a retrospective series collected from 18 cancer centers in 5 countries., Results: Forty patients (18 men, 22 women; median age, 60 years [range, 19-78]) were identified. Involvement of a cerebral hemisphere or deeper brain structures was seen in 37 patients, only leptomeningeal involvement in 2 patients, and spinal cord disease in 1 patient. Chemotherapy/radiotherapy was conducted in 15 patients, radiotherapy alone in 12, chemotherapy alone in 10, and tumor resection alone in 2, whereas 1 patient received no treatment. The median progression-free, disease-specific, and overall survival were 61.5 (range, 0-204), 130 (range, 1-204), and 79 (range, 1-204) months, respectively. Only age 60 years or older was associated with shorter progression-free (p = 0.009), disease-specific (p = 0.015), and overall survival (p = 0.001) in multivariate analysis., Interpretation: Low-grade primary central nervous system lymphoma differs from the high-grade subtype in its pathological, clinical, and radiological features. It has a better long-term outcome than primary central nervous system lymphoma in general with age 60 years or older adversely affecting survival.

Acute induction of oncogenic Ras provokes cellular senescence involving the retinoblastoma (Rb) pathway, but the tumour suppressive potential of senescence in vivo remains elusive. Recently, Rb-mediated silencing of growth-promoting genes by heterochromatin formation associated with methylation of histone H3 lysine 9 (H3K9me) was identified as a critical feature of cellular senescence, which may depend on the histone methyltransferase Suv39h1. Here we show that Emicro-N-Ras transgenic mice harbouring targeted heterozygous lesions at the Suv39h1, or the p53 locus for comparison, succumb to invasive T-cell lymphomas that lack expression of Suv39h1 or p53, respectively. By contrast, most N-Ras-transgenic wild-type ('control') animals develop a non-lymphoid neoplasia significantly later. Proliferation of primary lymphocytes is directly stalled by a Suv39h1-dependent, H3K9me-related senescent growth arrest in response to oncogenic Ras, thereby cancelling lymphomagenesis at an initial step. Suv39h1-deficient lymphoma cells grow rapidly but, unlike p53-deficient cells, remain highly susceptible to adriamycin-induced apoptosis. In contrast, only control, but not Suv39h1-deficient or p53-deficient, lymphomas senesce after drug therapy when apoptosis is blocked. These results identify H3K9me-mediated senescence as a novel Suv39h1-dependent tumour suppressor mechanism whose inactivation permits the formation of aggressive but apoptosis-competent lymphomas in response to oncogenic Ras.

Primary central nervous system lymphomas (PCNSL) are usually diffuse large B-cell non-Hodgkin's lymphomas (NHL). Here we characterize the clinical presentation, course and outcome of patients with low-grade PCNSL. Records of 332 patients screened for inclusion in three multicentre prospective trials were reviewed. Ten patients (3%) with a median age of 59 years and a median Karnofsky performance status of 70% were identified. Seven patients had B-cell and three had T-cell lymphoma. The median growth fraction was 4%. The radiological morphology was unusual for PCNSL in eight patients. Three patients underwent complete tumour resection, combined with chemotherapy in one patient and with chemotherapy plus local radiotherapy in another. Four patients received chemotherapy and three received chemotherapy plus whole-brain irradiation, resulting in four complete remissions, two no-change situations and one progressive disease. Patients had an overall survival (OAS) of 2-58+ months with a 2-year OAS of 67%. Low-grade PCNSL may differ from classical high-grade PCNSL in its clinical features and radiological morphology. The clinical course may be variable and frequently more indolent than in classical PCNSL.

Background: To determine the prognostic value of cell-cycle associated markers in ocular adnexal lymphoma (OAL)., Methods: Two hundred sixty-one consecutive cases of ocular adnexal lymphoproliferative lesions were subdivided into reactive lymphoid hyperplasia (RLH), atypical lymphoid hyperplasia (ALH) and OAL. The latter were sub-typed according to the new WHO Lymphoma Classification. All lesions were investigated applying standard immunohistochemical methods with antibodies specific for pRB, p53, p16, p21, BCL-6 and for multiple myeloma oncogene-1-protein (MUM1, also known as IRF4). The main endpoints included the development of a local recurrence, of systemic disease and of lymphoma-related death. The association of prognostic variables with endpoints was assessed by multiple logistic and Cox regression models, respectively., Results: The ocular adnexal lymphoproliferative lesions were categorised as OAL ( n=230; 88%), RLH ( n=29; 11%), and ALH ( n=2; 1%). The major lymphoma subtypes included 136 extranodal marginal zone B-cell lymphoma (EMZL), 31 diffuse large cell B-cell lymphomas, 27 follicular lymphomas, 9 plasmacytomas, 9 lymphoplasmocytic lymphoma/immunocytomas and 8 mantle cell lymphomas. The median follow-up time was 44.5 months. Most OAL patients had Stage IE disease and were treated with radiotherapy. Thirty-seven (25%) Stage IE patients had tumour relapses: these were significantly associated with an increased BCL6 blast percentage. Sixty-two (42%) Stage IE patients developed systemic disease: they had "non-EMZL" with large growth fractions and increased blast percentages for BCL6. Fifty-seven (25%) OAL patients died because of their lymphoma; lymphoma-related death was significantly associated on multivariable analysis with advanced clinical stage, an age >60 years and large tumour growth fractions., Conclusion: Subtyping of OAL according to the new WHO Lymphoma Classification, the stage of disease and tumour cell growth fraction aided the prediction of (1) tumour relapse, (2) the development of systemic disease and (3) lymphoma-related death in OAL.

The discrimination between lymphomas and reactive lymphoproliferations is difficult or even impossible in a proportion of cases by means of histology and additional immunhistochemistry alone. Therefore, the analysis of the clonality of the rearranged immunoglobulin genes and T-cell receptor genes, respectively, is often employed as an additional diagnostic tool. This analysis is based on the fact that the tumor cells of lymphomas harbor identically (clonally) rearranged antigen receptor genes whereas reactive lymphoproliferations consist of cells with differently (polyclonally or oligoclonally) rearranged antigen receptor genes. Initially Southern blot analysis was used to determine the presence of clonal lymphoid cell populations. Meanwhile polymerase chain reaction (PCR) is the method of choice because of its higher sensitivity and its applicability to DNA extracted from formalin-fixed tissues. Although this PCR approach appears to be simple, there are many pitfalls, which can lead to false negative or false positive results. In a diagnostic setting, these false clonality results could give rise to a wrong final diagnosis and, as a consequence, to the performance of an inadequate therapy. The reasons for the non-detectability of clonal B-cell or T-cell populations or for the detection of false clonality (e.g. clonal rearrangement pattern in the absence of a lymphoma) are manifold. In the following the most frequent reasons are discussed and recommendations are given to avoid false negative and false positive results.

Neoplasms of histiocytes and dendritic cells are rare, and their phenotypic and biological definition is incomplete. Seeking to identify antigens detectable in paraffin-embedded sections that might allow a more complete, rational immunophenotypic classification of histiocytic/dendritic cell neoplasms, the International Lymphoma Study Group (ILSG) stained 61 tumours of suspected histiocytic/dendritic cell type with a panel of 15 antibodies including those reactive with histiocytes (CD68, lysozyme (LYS)), Langerhans cells (CD1a), follicular dendritic cells (FDC: CD21, CD35) and S100 protein. This analysis revealed that 57 cases (93%) fit into four major immunophenotypic groups (one histiocytic and three dendritic cell types) utilizing six markers: CD68, LYS, CD1a, S100, CD21, and CD35. The four (7%) unclassified cases were further classifiable into the above four groups using additional morphological and ultrastructural features. The four groups then included: (i) histiocytic sarcoma (n=18) with the following phenotype: CD68 (100%), LYS (94%), CD1a (0%), S100 (33%), CD21/35 (0%). The median age was 46 years. Presentation was predominantly extranodal (72%) with high mortality (58% dead of disease (DOD)). Three had systemic involvement consistent with 'malignant histiocytosis'; (ii) Langerhans cell tumour (LCT) (n=26) which expressed: CD68 (96%), LYS (42%), CD1a (100%), S100 (100%), CD21/35 (0%). There were two morphological variants: cytologically typical (n=17) designated LCT; and cytologically malignant (n=9) designated Langerhans cell sarcoma (LCS). The LCS were often not easily recognized morphologically as LC-derived, but were diagnosed based on CD1a staining. LCT and LCS differed in median age (33 versus 41 years), male:female ratio (3.7:1 versus 1:2), and death rate (31% versus 50% DOD). Four LCT patients had systemic involvement typical of Letterer-Siwe disease; (iii) follicular dendritic cell tumour/sarcoma (FDCT) (n=13) which expressed: CD68 (54%), LYS (8%), CD1a (0%), S100 (16%), FDC markers CD21/35 (100%), EMA (40%). These patients were adults (median age 65 years) with predominantly localized nodal disease (75%) and low mortality (9% DOD); (iv) interdigitating dendritic cell tumour/sarcoma (IDCT) (n=4) which expressed: CD68 (50%), LYS (25%), CD1a (0%), S100 (100%), CD21/35 (0%). The patients were adults (median 71 years) with localized nodal disease (75%) without mortality (0% DOD). In conclusion, definitive immunophenotypic classification of histiocytic and accessory cell neoplasms into four categories was possible in 93% of the cases using six antigens detected in paraffin-embedded sections. Exceptional cases (7%) were resolvable when added morphological and ultrastructural features were considered. We propose a classification combining immunophenotype and morphology with five categories, including Langerhans cell sarcoma. This simplified scheme is practical for everyday diagnostic use and should provide a framework for additional investigation of these unusual neoplasms.

Recent years have brought an explosion of new diagnostic tools to the pathology of lymphomas, which have permitted more precise disease definition and recognition of factors that can predict prognosis and response to treatment. These new methods exploit both the biological features of normal lymphocytes as they progress through differentiation pathways and the genetic abnormalities that characterize malignant transformation. These features can be assessed in individual tumors with techniques that detect proteins (immunophenotyping), messenger RNA (in-situ hybridization), or changes in DNA [Southern blot, PCR, fluorescence in-situ hybridization (FISH), and gene sequencing]. Recently, the novel technology of "gene chips" or DNA microarrays has greatly enhanced the efficiency of analyzing expression of many genes simultaneously at the RNA level. Understanding the relationship of lymphoid neoplasms to their normal counterparts and the genetic events that lead to malignant transformation in lymphoid cells are essential for physicians caring for patients with lymphoma, since these are the basis of modern classification, diagnosis, and prognosis prediction. Although microarray technology is not ready for prime time in the daily diagnosis of lymphoma, practitioners should understand its potential and limitations. The vast majority of lymphoid neoplasms worldwide are derived from B lymphocytes at various stages of differentiation. The review by Harald Stein and colleagues present the events of normal B-cell differentiation that are relevant to understanding the biology of B-cell neoplasia. These include antigen receptor [immunoglobulin (Ig)] gene rearrangement, somatic mutations of the Ig variable region genes, receptor editing, Ig heavy chain class switch, and differential expression of a variety of adhesion molecules and receptor proteins as the cell progresses from a precursor B cell to a mature plasma cell. Most lymphoid neoplasms have genetic abnormalities, many of which appear to occur during the gene rearrangements and mutations that characterize normal B-cell differentiation. Dr. Riccardo Dalla Favera reviews the mechanisms of these translocations and other abnormalities, and their consequences for lymphocyte biology. The association of specific abnormalities with individual lymphomas is reviewed. Dr. Wing C. Chan reviews the technology and applications of DNA microarray analysis, its promises and pitfalls, and what it has already told us about the biology of lymphomas. Finally, what does this all mean? The applications, both current and future, of these discoveries to the diagnosis and treatment of patients with lymphoma are discussed by Dr. Nancy Lee Harris.

Paraffin blocks and clinical data from 521 patients with lymphocyte predominance Hodgkin disease (LPHD) diagnosed between 1970 and 1994 were collected from 16 European and United States oncological centers to establish the pathologic and clinical characteristics of a large patient cohort, to determine how frequent T-cell-rich large B-cell lymphoma (TCRLBCL) is among LPHD, and to find differential diagnostic criteria distinguishing between the 2 lymphoma categories. For this purpose, conventionally and immunohistologically stained sections were reviewed by a panel of hematopathologists. The diagnosis of LPHD was confirmed in only 219 of the 388 assessable cases (56.5%). This low confirmation rate was due mainly to the presence of a new variant of classical Hodgkin disease (CHD), which resembled, in terms of nodular growth and lymphocyte-richness, nodular LPHD and, in terms of the immunophenotype of the tumor cells, CHD and was designated nodular lymphocyte-rich CHD (NLRCHD). The nodules of LRCHD consisted-as in nodular LPHD-predominantly of B cells but differed from those present in LPHD in that they represented expanded mantle zones with atrophic germinal centers. Clinically, patients with LPHD and NLRCHD showed similar disease characteristics at presentation but differed in the frequency of multiple relapses and prognosis after relapse. Patients with LPHD and NLRCHD clearly differed from patients with CHD with nodular sclerosis or mixed cellularity, as they presented with an earlier disease stage and infrequent mediastinal involvement. As 97% of the LPHD cases showed a complete or partial nodular growth pattern, their differentiation from TCRLBCL was a rare problem in the present series. (Blood. 2000;96:1889-1899)

Most malignant tumours are classified according to their cellular origins. With regard to the classification of the malignant lymphomas, however, the application of this concept was not possible for a long period. Attitudes towards this changed rapidly with the discovery and description of the various cellular components of lymphoid tissue, and with the development of methods, which reliably distinguish the cells of the lymphoid system from each other. It has become apparent that the cellular origin of most lymphomatous diseases determines their respective morphological and clinical characteristics and, therefore, represents a sound basis for the classification of most lymphomas. This principle of classifying malignant lymphomas was initially applied by the Kiel Classification. Since itsí publication, further scientific discoveries have enabled us to close the gaps in our knowledge regarding the development of lymphoid tissue and cells. These advances were incorporated in the REAL Classification, and, subsequently, in the new WHO Classification. It is obvious, therefore, that an understanding of the malignant lymphomas and their classification requires a basic understanding of the differentiation of the cells of the lymphoid system. Consequently, a description of the components, the development and of the various developmental stages of the lymphoid cells will be briefly reviewed here, serving as a basis for the following chapters, which will summarise the characteristics of the different lymphomas. As the majority of the malignant lymphomas arise from B- and T-cells, these cell types will be concentrated upon in this review.

For decades, rival classification systems for malignant lymphoma that were hardly even comparable have existed side by side: the Kiel Classification has so far been used in the German-speaking parts of Europe and the "Working Formulation" mainly in the USA. At the beginning of the 1990's it became possible to overcome this unsatisfactory situation, when pathologists in the Old and New Worlds joined forces to elaborate a new classification for lymphoma, the Revised European-American Lymphoma (REAL) Classification, based on current scientific data. One new feature is the absence of a malignancy grading that is applicable to more than one entity. The system centres on the definition of distinct lymphomatous diseases that can be diagnosed with a high degree of reproducibility. Morphological and clinical characteristics are used for diagnosis, but so, consistently, are immuno-phenotypical and molecular genetic ones. An international cooperative study has confirmed the high reproducibility and clinical practicability of this tentative classification system. An international panel of pathologists appointed by the World Health Organization has updated the REAL classification, which is expected to be published in the updated version in 2001 under the title New WHO Classification. The articles that follow are based on the new WHO classification.

The advent of immunohistological and molecular techniques has enabled the comprehensive characterization of many lymphoma entities. Furthermore, it has increased the consensus in lymphoma classification among pathologists. In this review we describe the pathological features of primary intestinal lymphomas classified according to the revised European-American classification of lymphoid neoplasms. The majority of primary intestinal lymphomas are of B-cell lineage and most of these are high-grade tumors. By morphology they may be classified as diffuse large B-cell lymphomas of centroblastic, immunoblastic or plasmablastic type and Burkitt lymphomas. The latter occur predominantly in the terminal ileum and affect children or young adults. Low-grade extra-nodal marginal-zone lymphoma of the mucosa-associated lymphoid tissue (MALT) type and, less frequently, follicular center-cell lymphomas are the low-grade B-cell lymphomas most commonly observed in this region. The first mentioned tumor and its specific intestinal variant, alpha-chain disease or immunoproliferative small intestinal disease are well known for their indolent clinical course. Primary intestinal mantle-cell lymphoma often presents as multiple lymphomatous polyposis and similarly to its node-based equivalent is associated with an unfavorable prognosis. Most primary intestinal T-cell lymphomas display a characteristic immunophenotype, particular histological features with prominent epitheliotropism and are often associated with celiac disease indicating that these tumors form a specific lymphoma type. It has been termed intestinal T-cell lymphoma or enteropathy-type T-cell lymphoma. Clinically, these are aggressive diseases with a high mortality rate. In summary, primary intestinal lymphomas consist of several entities which display distinct clinicopathological features thus confirming the relevance of lymphoma typing.

Burkitt's lymphoma (BL) and Hodgkin's disease (HD) occurring in developing regions are frequently associated with Epstein-Barr virus (EBV) infection and have a high incidence in childhood. Recent genotyping studies indicate that the tumour cells of both neoplasms represent B cells that contain somatically mutated immunoglobulin heavy chain genes. This implies that the precursors of these neoplasms have participated in the germinal centre (GC) reaction. We therefore presumed that normal lymphoid tissues from children living in developing regions would harbour an increased number of EBV-infected cells within the GC, when compared with children living in industrialized nations. To test this hypothesis, hyperplastic tonsils from 40 children living in Bahia (Brazil) and 40 from German children were analysed for the presence of EBV-encoded small nuclear RNA (EBER) and EBV-encoded proteins by in situ hybridization and immunohistology, respectively. Although the overall EBV infection rate was similar in both groups (50 per cent of Bahian vs. 45 per cent of German cases), a significantly higher number of EBER-positive lymphoid cells were found in the GCs of 8/20 EBV-positive tonsils from Brazil (9-89 cells/GC; mean: 14.5 cells/GC per case), while only 3/18 tonsils from Germany displayed a few EBER positive cells (1-9 cells/GC; mean: 0.5 cell/GC per case) in this compartment (p < 0.007). In addition, the EBV-infected GC cells in Bahian samples resembled centroblasts, exhibited mitotic activity, and in two cases showed expression of EBV-encoded latent membrane protein (LMP)-1, findings not present in German samples. These data show that latently EBV-infected cells participate more frequently in GC reactions in developing regions than in industrialized countries and may abnormally express the oncogenic protein LMP-1. This could in part explain the higher incidence in this region of EBV association with lymphomas related to GC cells or their progeny, such as BL and HD.

Objective: Lymphoproliferative lesions of the ocular adnexa were analyzed to examine (1) the suitability of the Revised European-American Lymphoma (REAL) classification for the subtyping of the lymphomas in these sites; (2) the predictive value of the REAL classification for the evolution of these tumors; and (3) the frequency and prognostic impact of tumor type, location, proliferation rate (Ki-67 index), p53, CD5 positivity and the presence of monoclonality within these tumors., Design: Retrospective review., Methods: The clinical, histomorphologic, immunohistochemical, and molecular biologic (polymerase chain reaction [PCR]) features of lymphoid proliferations of the ocular adnexa were studied. STUDY MATERIALS: The ocular adnexal lymphoproliferative lesions were located as follows: orbit in 52 patients (46%), conjunctiva in 32 patients (29%), eyelid in 23 patients (21%), and caruncle in 5 patients (4%)., Results: Reactive lymphoid hyperplasia was diagnosed in 12 cases and lymphoma in 99 cases; 1 case remained indeterminate. The five main subtypes of lymphoma according to the REAL classification were extranodal marginal-zone B-cell lymphoma (64%), follicle center lymphoma (10%), diffuse large cell B-cell lymphoma (9%), plasmacytoma (6%), and lymphoplasmocytic lymphoma (5%). Age, gender, and anatomic localization of the lymphomas did not have prognostic significance during a follow-up period of 6 months to 16.5 years (mean, 3.3 years). Extent of disease at time of presentation was the most important clinical prognostic factor: advanced disease correlated with increased risk ratios of having persistent disease at the final follow-up and with lymphoma-related death (P < 0.001). Histomorphologic features and immunohistochemical markers positively correlating with disseminated disease at presentation, stage at final follow-up, and occurrence of lymphoma-related death included cytologic atypia (P < 0.001), MIB-1 proliferation rate (P < 0.001), and tumor cell p53 positivity (P < 0.001). The MIB-1 proliferation rates greater than 20% in extranodal marginal-zone B-cell lymphoma corresponded to at least stage II lymphoma (P < 0.05)., Conclusion: The REAL classification is suitable for the subdivision of the ocular adnexal lymphomas. The MIB-1 proliferation rate and p53 positivity may aid the prediction of disease stage and disease progression, whereas PCR can support the diagnosis and reduce the number of histologically indeterminate lesions.

Vascular endothelial growth factor (VEGF) is one of the main angiogenic cytokines in human solid tumours and inhibition of VEGF-induced angiogenesis suppresses tumour growth. Some groups of malignant lymphoma, including peripheral T-cell lymphomas and Hodgkin's disease, are characterized by a conspicuous proliferation of small vessels. To test the hypothesis that VEGF may also be involved in the angiogenesis in lymphomas and other lesions of the lymphoid system, VEGF expression was analysed in tissues, employing in situ hybridization with a 35S-labelled RNA probe specific for this cytokine. Significant expression of VEGF transcripts was observed in Hodgkin's disease and peripheral T-cell lymphomas, particularly of the angioimmunoblastic type. In contrast, expression of this cytokine was minimal or absent in follicle centre lymphoma and chronic lymphocytic leukemia of B-cell type. VEGF was mainly observed in reactive non-lymphoid CD68-negative cells, which probably represent fibroblasts or myofibroblasts. In normal and ulcerated tonsils, VEGF was expressed in the squamous epithelium but only rarely found in the lymphoid tissue. Although infectious mononucleosis tonsils contained high numbers of VEGF-positive cells in the interfollicular zone, expression of this cytokine was not found in Epstein-Barr virus (EBV)-infected cells, as determined by simultaneous in situ hybridization for VEGF and EBV-encoded small nuclear RNAs (EBER). In 5/8 cases of Castleman's disease, germinal centres containing small vessels also showed expression of VEGF, in contrast to normal tonsillar germinal centres which are devoid of both vessels and VEGF transcripts. It is concluded that VEGF may be involved in the induction of the angiogenesis of both peripheral T-cell lymphomas and Hodgkin's disease, but not in low-grade B-cell lymphomas. In contradistinction to solid tumours, in which this cytokine is commonly secreted by the tumour cells themselves, in malignant lymphoma VEGF is not a product of neoplastic cells. Vascularization of germinal centres in Castleman's disease may also be a consequence of abnormal local expression of VEGF.

Fifty formalin fixed, paraffin-embedded cases of T-acute lymphoblastic leukaemia (T-ALL) from 12 bone marrow trephines and 38 lymph nodes were stained with a new monoclonal antibody, 2TL 242, raised against recombinant TAL1 protein. The antibody recognizes TAL-1 polypeptides of molecular weight 39 and 41 kD (full length). In addition, a variety of other leukaemias and lymphomas were also stained with 2TL 242. Twenty-four of the 50 cases of T-ALL showed nuclear positivity, ranging from 10 to 90 per cent of leukaemic cells. A positive staining reaction was nuclear and stippled in pattern. Nuclear staining was not seen in any other type of leukaemia or lymphoma. Five cases of follicular lymphoma showed diffuse cytoplasmic staining of variable intensity. Although some background staining is obtained with this antibody, positive nuclear staining is easily distinguishable. This monoclonal antibody has a potential role in primary diagnosis and in the detection of minimal residual disease in T-ALL.

The Ber-ACT35 mAb was raised against the human T-cell lymphotrophic virus (HTLV) 1-transformed, CD4+ HUT 102 cell line and recognizes the human homologue of the OX40 (hOX40) antigen. The analysis of the expression of hOX40 by immunohistochemical techniques in malignant lymphomas, carcinomas and non-malignant tissues of different organs shows that hOX40 expression was almost completely restricted to T lymphocytes. Besides T cells only a small subpopulation of macrophages in Langerhans' cell histiocytosis and a few blasts in B-cell non-Hodgkin's lymphoma (B-NHL) revealed a faint immunostaining with the Ber-ACT35 mAb. Furthermore, most of the hOX40+ T-cells are CD4+.

To clarify whether mantle cell lymphomas (MCLs) are related to naive pre-germinal center B cells (expressing nonmutated rearranged VH genes) or to germinal center-derived memory B cells (expressing mutated rearranged VH genes), clonal IgH gene rearrangements using DNA from six MCLs were polymerase chain reaction (PCR)-amplified and analyzed for the presence of somatic mutations. For comparison, six cases of B-chronic lymphocytic leukemia (B-CLL) known to display nonmutated rearranged VH genes and six cases of follicle center lymphomas (FCLs) known to display mutated rearranged VH genes were included in our study. The VH region sequences of the six MCLs showed, like those of the six B-CLL cases, no or very little somatic mutations, in contrast to the VH sequences of the six FCL cases, all of which were highly mutated. This is indicative of MCL, like B-CLL, being derived from naive pre-germinal center B cells and furthermore underscores the postulated relationship of MCLs with the B cells of the normal follicular mantle zone because it has recently been shown that this mantle zone is solely or at least largely composed of naive (nonmutated) B cells.

An immunotoxin containing an anti-CD30 monoclonal antibody (Ber-H2) and saporin, a ribosome-inactivating protein type 1, is described. It specifically inhibits protein synthesis by Hodgkin derived target cell lines with a very high efficiency (IC50 ranging from 5 x 10(-12) M to 5 x 10(-14) M, as saporin), while irrelevant immunotoxins do not. Present results suggest that this immunotoxin could be used for in vivo therapy as well as for ex vivo bone marrow purging in Hodgkin's disease and CD30+ lymphomas.

In recent years, techniques, probes, and reagents became available to reliably visualize individual Epstein-Barr virus (EBV)-infected cells, to assess EBV gene expression, and to analyze the clonal composition of EBV genomes in human tissues. Application of these techniques to more than 1000 lymphoid tissue specimens revealed (1) characteristic cellular and compartmental distribution patterns of EBV-infected cells in normal lymph nodes, reflecting the interference of EBV with physiologic B cell differentiation pathways, (2) an association of EBV with various mono- and oligoclonal lymphoproliferations ranging from benign conditions to overtly malignant lymphomas, and (3) characteristic patterns of EBV gene expression among EBV-associated lymphoproliferations. In the context of the established immortalizing and transforming properties of EBV, the findings support the concept of an etiologic role of EBV for cases of certain lymphomas such as Burkitt's lymphoma, anaplastic large cell lymphoma, Hodgkin's disease, and lymphomas arising in immunocompromised individuals. In contrast, lymphomas harboring EBV in only proportions of the tumor cells (such as cases of peripheral T cell lymphoma and some B cell lymphoma types) argue against an etiologic role in the primary process of malignant transformation for the virus in these instances. Since in many of these cases a proportion of the EBV infected tumor cells express the EBV oncoprotein LMP (latent membrane protein) the virus may influence, however, the proliferative properties as well as the morphological and molecular phenotype of the neoplastic cells.

In a random HIV-seropositive population, malignant lymphomas were diagnosed in 31 patients, of whom 24 (77%) had non-Hodgkin lymphoma (NHL) and 7 (23%) Hodgkin lymphoma (HL). The prevalence of NHL among AIDS patients was 8% (23/279 cases), with a prevalence of 17% among autopsied patients (16/96 cases). No patient with HL had AIDS at the time of diagnosis. In 7 of 23 AIDS patients with NHL (30%) the diagnosis was made only post mortem; among these were all 5 patients with primary CNS NHL. Median survival from the time of diagnosis was 1 month for patients with NHL and 3 months for those with HL. In individual patients, survival for several years may be possible with chemotherapy. Certain patients with NHL appear to benefit from intensive chemotherapy with a combination of methotrexate, doxorubicin, cyclophosphamide, vincristine, prednisone, and bleomycin (MACOPB protocol). Appropriate, therapeutic strategies taking into account the patients' individual conditions, including the overall prognosis, urgently requires development. Metastatic CNS involvement, which was the primary cause of death in 5 of 11 patients with NHL (45%) receiving chemotherapy, represents a serious limitation to successful treatment.

Neuropathological findings from 8 individual cases of cerebral lymphomas in AIDS patients with consideration of the clinical, radiological, immunopathological, and other pertinent data selected from a series of 80 patients between 1985 and 1989 were studied. A wide variation in pathology was noted among our cases. It has been shown that lymphoma as a neuropathological diagnosis can coexist with a wide range of other characteristics, including toxoplasmosis, glial nodules, neuronophagia, degeneration, bleeding, hypoxia, progressive multifocal leucoencephalopathy, and myelopathy, although none of these attributes appeared more than casually interrelated. In general, the late-stage manifestations of lymphoma as were observed in this study, tended to be poorly localized, often simultaneously meningeal, perivascular, and diffuse in character. An important distinction between cerebral lymphomas of AIDS and non-AIDS patients is the highly atypical, clinically unreliable computer tomographic signals observed in several of our cases. Five of the six immunopathological investigations showed a preponderance of B-cell markers, corresponding in toto to high-grade non-Hodgkin lymphoma. One case exhibited immunohistological markers typical of Hodgkin's lymphoma (antibody CD-30). Of 6 obtainable serum specimens from our 8 cases, 4 showed high (greater than 2000) IgG titers against the EBNA-1 antigen of Epstein-Barr virus (EBV), of these three had IgM titers further supporting viral reactivation. One showed a normal IgG titer, yet with a significantly raised IgM titer.

The presence of Epstein-Barr virus (EBV) DNA and antigens was assessed by polymerase chain reaction and immunohistology, respectively, in a total of 92 cases of Hodgkin's disease, angioimmunoblastic lymphadenopathy, CD30-positive anaplastic large cell (ALC) lymphomas, and AIDS-associated atypical lymphoproliferations (ALP). Proportions of the EBV DNA-positive lesions showed latent membrane protein (LMP) expression; some of the LMP-positive ALC lymphomas and ALP cases also displayed EBNA2 immunostaining. BZLF1-protein and gp250/350 immunoreactivity were absent in all instances indicating latent EBV infection. Since the LMP gene has transforming potential, our findings support the concept of a pathoetiological role for EBV in these lymphoproliferative lesions.

Anaplastic large cell Ki-1 malignant lymphomas (MLs) resemble microvillous lymphoma in having a pleomorphic infiltrate with a prominent sinus growth pattern. Ultrastructural features of anaplastic large cell Ki-1 MLs and their immunologic relationship to the microvillous MLs have not been thoroughly evaluated. We have studied 23 anaplastic large cell Ki-1 MLs immunologically as well as 14 cases ultrastructurally, and compared them with 7 cases of microvillous MLs. Anaplastic large cell Ki-1 MLs were predominantly T-cell in type (13 cases) with three cases marking as B; in seven cases the immunophenotype was not clearly defined. Six microvillous MLs expressed monotypic cytoplasmic or surface immunoglobin and the remaining case had a probable B-cell phenotype (LN-1+, UCHL1-). All microvillous MLs were Ki-1/Ber-H2 (CD30) negative. Epithelial membrane antigen (EMA) marked most anaplastic large cell Ki-1 MLs, except those of B-cell type, whereas all microvillous MLs were EMA negative. By electron microscopy, both lymphomas had features of transformed lymphocytes although anaplastic large cell Ki-1 MLs generally had more nuclear irregularity and variability from cell to cell. Numerous cytoplasmic processes were present in three anaplastic large cell MLs and in all microvillous MLs. The ultrastructural features of the cytoplasmic projections were not sufficiently distinctive to differentiate these two lymphomas. It is apparent that at least two forms of MLs may have a sinus growth pattern and that these MLs cannot be differentiated by morphology alone. Full characterization requires a battery of immunological markers and ultrastructural studies; even then there is overlap of these MLs. The majority of microvillous MLs, are Ki-1-, EMA-, and have a B-cell phenotype, but a small population (21% in this study) of Ki-1+ MLs have numerous cytoplasmic processes. The biological and clinical significance of cytoplasmic projections in these lymphomas are unknown.

Monoclonal antibodies (mAbs) directed against the leucocyte common (CD45) antigen have been proposed as a useful tool for the differential diagnosis between malignant lymphomas (CD45+) and poorly differentiated nonhemopoietic tumors (CD45-). Thanks to the availability of mAbs directed against fixative-resistant epitopes of the CD45 molecule, this distinction can now easily be made even in routinely processed tissues. However, a small percentage of morphologically poorly defined neoplasms are difficult to diagnose even with the help of immunohistochemistry. The investigators report that 63 out of 165 anaplastic large-cell (ALC) lymphomas did not show any reactivity for the CD45 antigen in paraffin sections. In routine biopsies, the lymphomatous nature of these cases, most of which had been sent for consultation, could be always unequivocally established by demonstrating negativity for cytokeratins (mAb KL1) and clear dot-like and/or surface reactivity with the Ber-H2 mAb, which is directed against a fixative-resistant epitope of the lymphoid cell activation antigen CD30. Strikingly, 54% of the CD45-cases reacted with mAbs directed against fixative-resistant epitopes of the T cell-restricted CD45RO antigen (mAb UCHL1) or the B-restricted molecules CD45RA (mAb 4KB5) and L26 (unclustered). In order to avoid confusion of ALC lymphomas with anaplastic nonlymphoid tumors, pathologists must be aware of the existence of CD30+/CD45- ALC lymphomas, as they can mimic the above-mentioned malignancies both morphologically (due to the sinusoidal growth pattern) and phenotypically (due to the expression of EMA). The investigators conclude that the combined use of mAbs directed against fixative-resistant epitopes of the CD30, CD45RO, CD45RA, and L26 antigens and cytokeratins is essential for the correct diagnosis and treatment of these equivocal cases.

We describe 13 cases of a peculiar lymphoid tumour containing very large numbers of reactive histiocytes. The tumours occurred in young patients (mean age 14.8 y) who presented with systemic symptoms and superficial lymphadenopathy. Microscopic examination revealed a diffuse effacement of lymph node structure due to the presence of histiocytes intermingled with a variable number of anaplastic large lymphoid cells. The latter, in some cases, were isolated, while in others they were arranged in clusters or were diffusely present in residual sinuses. The large anaplastic cells expressed the activation markers CD30 (Ki-1), CD25 (interleukin-2 receptor), CD70 (Ki-24) and Ki-27, as well as varying combinations of T-associated molecules. The histiocytes expressed lysozyme and the CD11b (C3bi-R), CD11c (p150, 95) CD14, CD68 (KPI) and Ber-Mac3 antigens. Double staining with the antibody Ki-67 demonstrated that the proliferating components were the CD30-positive cells and not the histiocytes. T-cell receptor beta gene rearrangements were shown in three cases tested. The patients responded well to aggressive chemotherapy and nine are still alive, eight in complete remission. It is suggested that the tumour represents a well-defined clinico-pathological entity originating from activated T-lymphocytes.

In a previous study employing conventional immunological marker analysis we found that 17% of high grade malignant lymphomas were devoid of cytoplasmic and membrane immunoglobulin and also sheep erythrocyte receptors. Cryostat sections from 24 of these cases (four of low grade and 20 of high grade malignancy) were stained with a panel of 30 monoclonal antibodies and six polyclonal antisera using a sensitive immunoperoxidase method. All tumours expressed the leucocyte common antigen (detected by monoclonal antibody 2D1) and all lacked epithelial cytokeratin (monoclonal antibody LE61), confirming their haematopoietic origin. All but one of the lymphomas expressed antigens characteristic of either B cells (17 cases) or T cells (six cases), while one case (morphologically a centroblastic lymphoma) had an unusual dual phenotype in which strong staining for T6 (marker of immature T cells) was associated with expression of the pan B lymphocyte antigens detectable with To15, anti-B1, anti-Leu12. This case was therefore classified as a B cell lymphoma showing aberrant expression of the T6 antigen. The pan B cell antibodies (To15, anti-B1, anti-Leu12) all appeared highly specific and sensitive, but the simultaneous use of all three monoclonal antibodies was necessary to detect the B cell nature in each of the 18 lymphomas. A wider panel of monoclonal antibodies was required to detect T lymphomas since these often disclosed atypical and restricted phenotypes. To15 and UCHT1 were the most reliable antibodies for the detection of B and T cell neoplasms, respectively. We conclude that most, if not all, "non-B, non-T" lymphomas are of either B or T lymphocyte origin and that monoclonal antibodies provide indispensable tools in their classification and diagnosis.

This paper describes the use of a panel of seven monoclonal antibodies (selected so as to include reagents reactive with both epithelial and lymphoid cells) for distinguishing between anaplastic carcinoma and high grade lymphoma. Details are given of the immunohistological reactions of these antibodies against a wide range of both normal and malignant tissues and of a number of practical instances in which use of the antibody panel enabled a diagnosis to be made when routine histological examination had been inconclusive.