PDGFRß promotes oncogenic progression via STAT3/STAT5 hyperactivation in anaplastic large cell lymphoma.

BACKGROUND: Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkin T cell lymphoma commonly driven by NPM-ALK. AP-1 transcription factors, cJUN and JUNb, act as downstream effectors of NPM-ALK and transcriptionally regulate PDGFRß. Blocking PDGFRß kinase activity with imatinib effectively reduces tumor burden and prolongs survival, although the downstream molecular mechanisms remain elusive. METHODS AND RESULTS: In a transgenic mouse model that mimics PDGFRß-driven human ALCL in vivo, we identify PDGFRß as a driver of aggressive tumor growth. Mechanistically, PDGFRß induces the pro-survival factor Bcl-xL and the growth-enhancing cytokine IL-10 via STAT5 activation. CRISPR/Cas9 deletion of both STAT5 gene products, STAT5A and STAT5B, results in the significant impairment of cell viability compared to deletion of STAT5A, STAT5B or STAT3 alone. Moreover, combined blockade of STAT3/5 activity with a selective SH2 domain inhibitor, AC-4-130, effectively obstructs tumor development in vivo. CONCLUSIONS: We therefore propose PDGFRß as a novel biomarker and introduce PDGFRß-STAT3/5 signaling as an important axis in aggressive ALCL. Furthermore, we suggest that inhibition of PDGFRß or STAT3/5 improve existing therapies for both previously untreated and relapsed/refractory ALK+ ALCL patients.

SPARC-positive macrophages are the superior prognostic factor in the microenvironment of diffuse large B-cell lymphoma and independent of MYC rearrangement and double-/triple-hit status.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease with respect to outcome. Features of the tumor microenvironment (TME) are associated with prognosis when assessed by gene expression profiling. However, it is uncertain whether assessment of the microenvironment can add prognostic information to the most relevant and clinically well-established molecular subgroups when analyzed by immunohistochemistry (IHC). PATIENTS AND METHODS: We carried out a histopathologic analysis of biomarkers related to TME in a very large cohort (n = 455) of DLBCL treated in prospective trials and correlated with clinicopathologic and molecular data, including chromosomal rearrangements and gene expression profiles for cell-of-origin and TME. RESULTS: The content of PD1+, FoxP3+ and CD8+, as well as vessel density, was not associated with outcome. However, we found a low content of CD68+ macrophages to be associated with inferior progression-free survival (PFS) and overall survival (OS; P = 0.023 and 0.040, respectively) at both univariable and multivariable analyses, adjusted for the factors of the International Prognostic Index (IPI), MYC break and BCL2/MYC and BCL6/MYC double-hit status. The subgroup of PDL1+ macrophages was not associated with survival. Instead, secreted protein acidic and cysteine rich (SPARC)-positive macrophages were identified as the subtype of macrophages most associated with survival. SPARC-positive macrophages and stromal cells directly correlated with favorable PFS and OS (both, P[log rank] <0.001, P[trend] < 0.001). The association of SPARC with prognosis was independent of the factors of the IPI, MYC double-/triple-hit status, Bcl2/c-myc double expression, cell-of-origin subtype and a recently published gene expression signature [lymphoma-associated macrophage interaction signature (LAMIS)]. CONCLUSIONS: SPARC expression in the TME detected by a single IHC staining with fair-to-good interobserver reproducibility is a powerful prognostic parameter. Thus SPARC expression is a strong candidate for risk assessment in DLBCL in daily practice.

First-line treatment with R-CHOP or rituximab-bendamustine in patients with follicular lymphoma grade 3A-results of a retrospective analysis.

Based on centroblast frequency, follicular lymphoma (FL) is subdivided into grades 1-2, 3A, and 3B. Grade FL3A frequently coexists with FL1-2 (FL1-2-3A). Based on clinical trials, FL1-2 is treated with rituximab (R) or obinutuzumab plus bendamustine (B) or CHOP, while FL3B is treated with R-CHOP. In contrast, there are little data guiding therapy in FL3A. We present a retrospective, multicenter analysis of 95 FL3A or FL1-2-3A and 203 FL1-2 patients treated with R-CHOP or R-B first-line. R-CHOP facilitated a higher response rate (95% versus 76%) and longer overall survival (OS) (3-year OS 89% versus 73%, P = 0.008) in FL3A or FL1-2-3A, whereas the difference in progression-free survival (PFS) did not reach statistical significance. While transformation rates into aggressive lymphoma were similar between both groups, there were more additional malignancies after R-B compared with R-CHOP (6 versus 2 cases). In FL1-2, R-B achieved a higher 3-year PFS (79% versus 47%, P < 0.01), while there was no significant difference regarding OS or transformation. With the limitations of a retrospective analysis, these results suggest a benefit for R-CHOP over R-B in FL3A or FL1-2-3A. Confirmatory data from prospective clinical trials are needed.

Only strongly enhanced residual FDG uptake in early response PET (Deauville 5 or qPET ≥ 2) is prognostic in pediatric Hodgkin lymphoma: Results of the GPOH-HD2002 trial.

PURPOSE: In 2014, we published the qPET method to quantify fluorodeoxyglucose positron emission tomography (FDG-PET) responses. Analysis of the distribution of the quantified signals suggested that a clearly abnormal FDG-PET response corresponds to a visual Deauville score (vDS) of 5 and high qPET values ≥ 2. Evaluation in long-term outcome data is still pending. Therefore, we analyzed progression-free survival (PFS) by early FDG-PET response in a subset of the GPOH-HD2002 trial for pediatric Hodgkin lymphoma (PHL). PATIENTS/METHODS: Pairwise FDG-PET scans for initial staging and early response assessment after two cycles of chemotherapy were available in 93 PHL patients. vDS and qPET measurement were performed and related to PFS. RESULTS: Patients with a qPET value ≥ 2.0 or vDS of 5 had 5-year PFS rates of 44%, respectively 50%. Those with qPET values < 2.0 or vDS 1 to 4 had 5-year PFS rates of 90%, respectively 80%. The positive predictive value of FDG-PET response assessment increased from 18% (9%; 33%) using a qPET threshold of 0.95 (vDS ≤ 3) to 30% (13%; 54%) for a qPET threshold of 1.3 (vDS ≤ 4) and to 56% (23%; 85%) when the qPET threshold was ≥ 2.0 (vDS 5). The negative predictive values remained stable at ≥92% (CI: 82%; 98%). CONCLUSION: Only strongly enhanced residual FDG uptake in early response PET (vDS 5 or qPET ≥ 2, respectively) seems to be markedly prognostic in PHL when treatment according to the GPOH-HD-2002 protocol is given.

[Hematological neoplasias as differential diagnoses of soft tissue tumors]. / Hämatologische Neoplasien als Differenzialdiagnosen von Weichgewebstumoren.

BACKGROUND: Several hematological malignancies might morphologically present as differential diagnoses of sarcomas. OBJECTIVES: To illustrate entities of hematological malignancies that might cause difficulties in differentiation from sarcomas and to introduce immunohistochemical and molecular tests that facilitate the diagnosis. MATERIAL AND METHODS: Selective literature research ( http://www.ncbi.nlm.nih.gov ) was combined with the clinico-pathological experience of the authors. RESULTS: In particular, hematologic malignancies with small blue round cell cytology, as well as lymphomas with anaplastic or spindle cell morphology, may mimic sarcomas. Identification of the correct diagnosis is usually possible by applying immunohistochemical and molecular analyses. Lymphomas without expression of CD45 and hematological neoplasias with expression of markers characteristic of sarcomas may cause difficulties in differential diagnosis. CONCLUSION: Hematological malignancies should be kept in mind as differential diagnoses of sarcomas and should be excluded by immunohistochemical and molecular analyses according to morphology and the clinical picture.

[Aggressive B­cell lymphomas : Recommendations from the German Panel of Reference Pathologists in the Competence Network on Malignant Lymphomas on diagnostic procedures according to the current WHO classification, update 2017]. / Aggressive B­Zell-Lymphome : Empfehlungen des Deutschen Panels der Referenzpathologen im Kompetenznetz Maligne Lymphome e. V. zum diagnostischen Vorgehen nach der aktuellen WHO-Klassifikation, Update 2017.

The update of the 4th edition of the WHO classification for hematopoietic neoplasms introduces changes in the field of mature aggressive B­cell lymphomas that are relevant to diagnostic pathologists. In daily practice, the question arises of which analysis should be performed when diagnosing the most common lymphoma entity, diffuse large B­cell lymphoma. We discuss the importance of the cell of origin, the analysis of MYC translocations, and the delineation of the new WHO entities of high-grade B­cell lymphomas.

[Revised version of the 4th edition of the WHO classification of malignant lymphomas : What is new?] / Revidierte Fassung der 4. Ausgabe der WHO-Klassifikation maligner Lymphome : Was ist neu?

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 B­cell lymphomas. Important new diagnostic categories include the high-grade B­cell lymphomas, the large B­cell 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 T­cell lymphoproliferative disorder of the gastrointestinal tract, has been strengthened. Finally, diagnostic criteria for existing lymphoma entities have been refined.

Molecular signatures that can be transferred across different omics platforms.

MOTIVATION: Molecular signatures for treatment recommendations are well researched. Still it is challenging to apply them to data generated by different protocols or technical platforms. RESULTS: We analyzed paired data for the same tumors (Burkitt lymphoma, diffuse large B-cell lymphoma) and features that had been generated by different experimental protocols and analytical platforms including the nanoString nCounter and Affymetrix Gene Chip transcriptomics as well as the SWATH and SRM proteomics platforms. A statistical model that assumes independent sample and feature effects accounted for 69-94% of technical variability. We analyzed how variability is propagated through linear signatures possibly affecting predictions and treatment recommendations. Linear signatures with feature weights adding to zero were substantially more robust than unbalanced signatures. They yielded consistent predictions across data from different platforms, both for transcriptomics and proteomics data. Similarly stable were their predictions across data from fresh frozen and matching formalin-fixed paraffin-embedded human tumor tissue. AVAILABILITY AND IMPLEMENTATION: The R-package 'zeroSum' can be downloaded at https://github.com/rehbergT/zeroSum . Complete data and R codes necessary to reproduce all our results can be received from the authors upon request. CONTACT: rainer.spang@ur.de.

[Recovery of paraffin blocks and central archiving : Experiences of the Kiel lymph node registry and the German study group for Hodgkin lymphoma]. / Rückforderung von Paraffinblöcken und zentrale Archivierung : Erfahrungen des Lymphknotenregisters Kiel und der Deutschen Studiengruppe für Hodgkin Lymphome.

BACKGROUND: Central collection of tissue blocks for pathological and translational research is particularly important in rare diseases. Transfer of tissue blocks from primary to central pathology is of crucial importance. OBJECTIVES: We aimed to answer the following questions: Has the transfer of tissue blocks sent for consultation or within clinical trials changed over the last 20 years? What are the reasons for reclaiming tissue blocks by the primary pathology and what actions would convince primary pathologists to leave the blocks in the reference pathology? MATERIAL AND METHODS: The first 100 biopsies of each year between 1995 and 2015 (n = 2100), as well as all tissue transfers within therapeutic studies (n = 1405, German Hodgkin Study Group, GHSG) between 1998 and 2015, were analyzed separately for block reclaims using the Department of Pathology database. A questionnaire evaluated the reasons for block reclaiming by the peripheral pathologists. RESULTS: There is a significant increase in block reclaims during the period analyzed among submissions for consultation as well as in clinical trials (linear regression, p = 0.0195 and p = 0.0107). The percentage of block reclaims does not differ between consultations and cases submitted upon request within clinical trials (p = 0.2404, t-test). A survey among pathologies that reclaim the block showed that their willingness to leave the block at the reference center would increase if the compatibility with accreditation guidelines (39.3%), a positive statement from professional associations (25%), or a formal confirmation of availability (53.6%) is provided. DISCUSSION: In particular, to improve research on rare diseases, it is desirable to point out the compatibility of central archiving in a designated center with accreditation guidelines.

Clinical, pathological and genetic features of follicular lymphoma grade 3A: a joint analysis of the German low-grade and high-grade lymphoma study groups GLSG and DSHNHL.

BACKGROUND: Histologically, follicular lymphoma (FL) grades 1, 2 and 3A are composed of two distinct cell types, centroblasts and centrocytes. FL grade 3B is composed only of centroblasts and has been shown to differ in immunophenotype and genetics from FL that contain centrocytes. We aimed to understand the pathogenetic and clinical relation between FL grade 3A to FL grade 1/2 on the one hand and FL grade 3B on the other hand. PATIENTS AND METHODS: Trial patients with long-term follow-up and diagnosis of FL grade 3 were selected and samples underwent a second central pathological review using a multiple-observer approach to assess grading. RESULTS: Interobserver variability for diagnosing FL grade 3 was high. FL grade 3A frequently harbored areas of FL grade 1/2 within the same tissue specimen. FL grade 3B rarely coexisted with grade 1/2 or 3A, suggesting divergent pathogenesis. There was no statistically significant difference in outcome between 47 cases of FL grade 3A and 14 cases of grade 3B. Compared with grade 1/2 FL, both groups showed longer progression-free survival without late events, especially after immunochemotherapy; this outcome difference was retained after adjustment for clinical prognostic factors. The subgroup of FL grade 3A with an additional FL grade 1/2 component or a translocation t(14;18) showed a poorer outcome. In contrast, the FL grade 3A lacking t(14;18) and of localized stage resembled the pediatric type of FL and showed a very good outcome. FL3 with MYC breaks showed a poor outcome. CONCLUSIONS: The results suggest that first-line immunochemotherapy might allow long-lasting remissions in a subgroup of FL grade 3A similar to diffuse large B-cell lymphoma. Within FL3A, prognostic subgroups can be identified by analyzing for coexisting FL1/2 and MYC breaks.

[Classification of malignant lymphomas. Current situation]. / Klassifikation maligner Lymphome. Aktueller Stand.

BACKGROUND: The World Health Organization (WHO) is planning an update of the WHO classification of malignant lymphomas. OBJECTIVE: To present new findings concerning the diagnostics and subclassification of malignant lymphomas. MATERIAL AND METHODS: A selective literature search ( http://www.ncbi.nlm.nih.gov ) was carried out and combined with the practical experiences of the authors in clinicopathological diagnostics. RESULTS: In recent years an increasing number of early lesions of malignant lymphomas have been described but the potential malignancy of these lesions is at least for some entities still uncertain. Newly defined entities have been described within the group of T-cell lymphomas and prognostic subgroups have been identified in the heterogeneous group of diffuse large B-cell lymphomas. Detection of mutations facilitates the differential diagnostics of morphologically similar diseases and can be an important component of the diagnostics. CONCLUSION: Recent scientific insights are being included more and more into the diagnostics of lymphomas. The update of the WHO classification is a consequence of these developments.

Treatment of older patients with mantle-cell lymphoma.

BACKGROUND: The long-term prognosis for older patients with mantle-cell lymphoma is poor. Chemoimmunotherapy results in low rates of complete remission, and most patients have a relapse. We investigated whether a fludarabine-containing induction regimen improved the complete-remission rate and whether maintenance therapy with rituximab prolonged remission. METHODS: We randomly assigned patients 60 years of age or older with mantle-cell lymphoma, stage II to IV, who were not eligible for high-dose therapy to six cycles of rituximab, fludarabine, and cyclophosphamide (R-FC) every 28 days or to eight cycles of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) every 21 days. Patients who had a response underwent a second randomization to maintenance therapy with rituximab or interferon alfa, each given until progression. RESULTS: Of the 560 patients enrolled, 532 were included in the intention-to-treat analysis for response, and 485 in the primary analysis for response. The median age was 70 years. Although complete-remission rates were similar with R-FC and R-CHOP (40% and 34%, respectively; P=0.10), progressive disease was more frequent with R-FC (14%, vs. 5% with R-CHOP). Overall survival was significantly shorter with R-FC than with R-CHOP (4-year survival rate, 47% vs. 62%; P=0.005), and more patients in the R-FC group died during the first remission (10% vs. 4%). Hematologic toxic effects occurred more frequently in the R-FC group than in the R-CHOP group, but the frequency of grade 3 or 4 infections was balanced (17% and 14%, respectively). In 274 of the 316 patients who were randomly assigned to maintenance therapy, rituximab reduced the risk of progression or death by 45% (in remission after 4 years, 58%, vs. 29% with interferon alfa; hazard ratio for progression or death, 0.55; 95% confidence interval, 0.36 to 0.87; P=0.01). Among patients who had a response to R-CHOP, maintenance therapy with rituximab significantly improved overall survival (4-year survival rate, 87%, vs. 63% with interferon alfa; P=0.005). CONCLUSIONS: R-CHOP induction followed by maintenance therapy with rituximab is effective for older patients with mantle-cell lymphoma. (Funded by the European Commission and others; ClinicalTrials.gov number, NCT00209209.).

[Diagnostic molecular pathology of lymphatic and myeloid neoplasms]. / Diagnostische Molekularpathologie bei lymphatischen und myeloischen Neoplasien.

Molecular pathology has been an integral part of the diagnostics of tumors of the hematopoietic system substantially longer than for solid neoplasms. In contrast to solid tumors, the primary objective of molecular pathology in hematopoietic neoplasms is not the prediction of drug efficacy but the diagnosis itself by excluding reactive proliferation and by using molecular features for tumor classification. In the case of malignant lymphomas, the most commonly applied molecular tests are those for gene rearrangements for immunoglobulin heavy chains and T-cell receptors. However, this article puts the focus on new and diagnostically relevant assays in hematopathology. Among these are mutations of MYD88 codon 265 in lymphoplasmacytic lymphomas, B-raf V600E in hairy cell leukemia and Stat3 exon 21 in indolent T-cell lymphomas. In myeloproliferative neoplasms, MPL W515, calreticulin exon 9 and the BCR-ABL and JAK2 V617F junctions are the most frequently analyzed differentiation series. In myelodysplastic and myeloproliferative neoplasms, SRSF2, SETBP1 and CSF3R mutations provide important differential diagnostic information. Genes mutated in myelodysplastic syndromes (MDS) are particularly diverse but their analysis significantly improves the differential diagnostics between reactive conditions and MDS. The most frequent changes in MDS include mutations of TET2 and various genes encoding splicing factors.

[Histiocytic diseases in childhood and adolescence]. / Histiozytäre Erkrankung des Kindes- und Jugendalters.

Histiocytic diseases are generally rare with a variable clinical course and variable morphology which often have a peak frequency of occurrence in childhood and adolescence. Histiocytoses are subdivided into Langerhans cell histiocytosis and the so-called non-Langerhans cell histiocytosis, such as juvenile xanthogranuloma, Erdheim-Chester disease and Rosai-Dorfman disease. The most common forms of histiocytosis in childhood are Langerhans cell histiocytosis and juvenile xanthogranuloma. In contrast, forms of histiocytosis which occur more frequently in adulthood, such as Erdheim-Chester disease and Rosai-Dorfman disease are rare in childhood. Some forms of histiocytosis harbor BRAFv600E mutations. In Langerhans cell histiocytosis they have been found in 50-55 % of the cases examined and in Erdheim-Chester disease in up to 100 % of cases. In the remaining forms of histiocytosis (especially juvenile xanthogranuloma and Rosai-Dorfman disease) BRAF mutations could not be detected. A prognostic relevance could not be shown so far; however, in individual cases a mutation analysis of BRAF could provide help in the differential diagnostic considerations or the option of a therapy approach with BRAF inhibitors.

[Malignant lymphomas in children and adolescents. Practical knowledge for diagnosis]. / Maligne Lymphome im Kindes- und Jugendalter : Praktisches Wissen für den diagnostischen Alltag.

Malignant lymphomas are very rare in childhood. Therefore in Germany and Europe-wide the diagnosis and treatment of these diseases and research into them are carried out in multicenter-study groups and registries that provide central clinical consulting as well as histopathological, genetic, and molecular diagnoses. Despite these central structures, the diagnosis of these aggressive lymphomas is usually made initially outside these specialized centers. Therefore, in clinical situations that are often quite critical, every pathologist may be required to make the initial diagnosis and decide on the initial therapy regimen. Specific features related to the incidence, biology, and clinical presentation of pediatric lymphomas strongly influence the diagnostic workup and require a different diagnostic procedure from that employed in adults. In this paper, we will try to provide the most important information required for a tissue-saving initial diagnosis of the most common pediatric lymphomas. The proposed procedures allow reliable differentiation into the main lymphoma categories and, thus, provide the necessary information for the first therapeutic regimens, although the final subtyping will remain the responsibility of specialists. The most relevant histopathological features, appropriate immunohistochemical stains, and diagnostic pitfalls are demonstrated. As examples of the most common entities, special attention is paid to Burkitt lymphoma, diffuse large B-cell lymphoma, precursor T- and B-cell lymphoma, and anaplastic large-cell lymphoma.

Surgical impact of new treatments in breast cancer.

Local treatment of breast cancer with tumor-free surgical margins is the standard procedure in the treatment of T1 and small T2 breast cancers. Surgery is followed by radiation therapy, and adjuvant systemic therapy is offered depending on primary tumor characteristics, such as tumor size, grade of differentiation, number of involved axillary lymph nodes, the status of estrogen (ER) and progesterone (PR) receptors, and the expression of the human epidermal growth factor 2 (HER2) receptor. Although this approach implies a higher risk of ipsilateral breast tumor recurrence, the total risk of recurrence is low (1% per year), with rates of overall survival similar to that after radical procedures. The most peripheral part of epithelial tumors, the tumor margin, is the part which is most likely to remain in loco after surgical resection. Thus, understanding the biology of the invasion front is important as these tumor cells have been reported to lose epithelial properties, such as cohesiveness and keratin expression, and to acquire features of mesenchymal cells. The parallel appearance of tumor cells in different states of cell dedifferentiation implicates a dynamic equilibrium that is determined by the induction of epithelial-mesenchymal transition (EMT). EMT has been suggested to be of prime importance for tissue and vessel invasion. Furthermore, features of EMT are associated with the activity of tumor stem cells (TSC). TSC exist in breast cancer and their appearance varies depending on the used marker profile. Consequently, intratumoral heterogeneity is reflected by the grade of EMT activation. A specific function at the invasion front is hypothesized but has not yet been proven. Nevertheless, the molecular differentiation between the tumor center and the invasion front enhances the importance of tumor-free surgical margins.

[Mycosis fungoides or inflammatory dermatitis: differential diagnosis between early lymphoma and inflammation in skin biopsies]. / Mycosis fungoides oder entzündliche Dermatose: Differenzialdiagnostik zwischen frühem Lymphom und Entzündung an der Hautbiopsie.

Mycosis fungoides is a cutaneous T-cell lymphoma with protracted clinical course and progression in different stages with increasing aggressiveness. The clinical picture as well as the histopathology of mycosis fungoides within the early patch and plaque phase is difficult to delineate from some inflammatory skin diseases. Thus, the diagnosis of these early stages of the lymphoma is only possible when clinical, histopathological, and molecular features are integrated into the diagnosis, especially as none of the individual disease criteria is specific. Important clues towards the diagnosis of mycosis fungoides are cytologically abnormal epidermotropic CD4-positive T-cells causing only minor epidermal alterations, the formation of Pautrier-abscesses and basal alignment of the epidermotropic T-cells. The findings of an aberrant T-cell immunophenotype of the intraepidermal lymphoid component as well as the molecular proof of T-cell clonality are important further features. In the differential diagnosis between early stage mycosis fungoides and parapsoriasis, there remains nevertheless a diagnostic and maybe also a true biological grey zone.

[Differential diagnosis of lymphoid infiltrates in the central nervous system: experience of the Network Lymphomas and Lymphomatoid Lesions in the Nervous System]. / Differenzialdiagnose lymphoider Infiltrate im Zentralnervensystem : Erfahrungen des Netzwerks Lymphome und lymphomatoide Läsionen des Nervensystems.

The differential diagnosis of lymphoid lesions in the central nervous system covers a broad spectrum of neoplastic and inflammatory disorders. Complex cases benefit from the combined expertise in the fields of hematopoietic and neuroepithelial tumors as well as neuroimmunology. The Network Lymphomas and Lymphomatoid Lesions in the Nervous System (NLLLN) recommends performing a biopsy prior to any therapeutic intervention as a precise diagnosis was impossible in approximately 50 % of patients pretreated with corticosteroids. This is based on the analysis of approximately 1,000 cases in the past 4 years. In addition to total NLLLN experiences the characteristics, pathogenesis and differential diagnosis of primary lymphoma of the central nervous system are discussed.