Cases Of Primary Mediastinal Large B-cell Lymphoma Research Articles

Molecular Characterization of Primary Mediastinal Large B-Cell Lymphomas.

Since the description of primary mediastinal large B-cell lymphoma (PMBL) as a distinct entity from diffuse large B-cell lymphomas (DLBCL), numerous studies have made it possible to improve their definition. Despite this, this differential diagnosis can be challenging in daily practice. However, in some centers, PMBL may be treated according to a particular regimen, distinct from those used in DLBCL, emphasizing the importance of accurate identification at diagnosis. This study aimed to describe the histological and molecular characteristics of PMBL to improve the accuracy of their diagnosis. Forty-nine cases of PMBL were retrospectively retrieved. The mean age at diagnosis was 39 years (21-83), with a sex ratio of 0.88. All cases presented a fibrous background with diffuse growth of intermediate to large cells with an eosinophil (26/49, 53%) or retracted cytoplasm (23/49, 47%). "Hodgkin-like" cells were observed in 65% of cases (32/49, 65%). The phenotype was: BCL6+ (47/49, 96%), MUM1+ (40/49, 82%), CD30+ (43/49, 88%), and CD23+ (37/49, 75%). Genomic DNAs were tested by next generation sequencing of 33 cases using a custom design panel. Pathogenic variants were found in all cases. The most frequent mutations were: SOCS1 (30/33, 91%), TNFAIP3 (18/33, 54.5%), ITPKB (17/33, 51.5%), GNA13 (16/33, 48.5%), CD58 (12/33, 36.4%), B2M (12/33; 36.4%), STAT6 (11/33, 33.3%) as well as ARID1A (10/33, 30.3%), XPO1 (9/33, 27.3%), CIITA (8/33, 24%), and NFKBIE (8/33, 24%). The present study describes a PMBL cohort on morphological, immunohistochemical, and molecular levels to provide pathologists with daily routine tools. These data also reinforce interest in an integrated histomolecular diagnosis to allow a precision diagnosis as early as possible.

A Digital Gene-Expression Signature Supports Mediastinal Gray Zone Lymphoma Stratification within Classical Hodgkin or Primary Mediastinal B-Cell Lymphoma

Mediastinal non-Hodgkin Lymphomas with intermediate features between Primary Mediastinal Large B-cell Lymphoma (PMBCL) and classical Hodgkin Lymphoma (cHL) - also known as mediastinal Gray Zone Lymphomas (mGZL) - represent a unique, diagnostically challenging entity (Khoury et al., Leukemia 2022). They typically exhibit discordant morpho-phenotypical characteristics between cHL and PMBCL, a high rate of diagnostic reclassification and consequent poor therapeutic outcomes. While a comprehensive biological picture of this entity remains to be fully deciphered, recent gene expression profiling of mGZL confirmed their molecular straddling between cHL and PMBCL (Pittaluga et al., Blood Cancer Discov., 2020; Sarkozy et al., BLOOD ADVANCES, 2020). However, the diagnosis of mGZL is still challenging and largely based on the satisfaction of morphological and immunophenotypic criteria. Therefore, there is an urgent need of practical tools exploiting deeper molecular traits of mGZL to facilitate their pathological boundaries between cHL or PMBCL and selection of proper treatment. We applied CIBERSORTx (Newman et al., Nat. Biotechnol., 2019) to public Gene Expression Profiling (GEP) data of a training set comprising 50 cHL (GSE17920) and 31 PMBCL (GSE11318). Such approach purified GEP of both tumor and microenvironment (TME) origin, followed by a Nonnegative Matrix Factorization (NMF)-based selection of 2,913 genes with high discriminating capacity between the two lymphoma subtypes. After a fine-tuned feature selection, a final signature of 168 genes was verified on the training cohort, tested in silico on an independent series of 34 cHL (GSE17920) and 20 PMBCL (GSE87371), and finally validated by NanoString technology on a real-life (RL) cohort including ten cHL and twelve PMBCL to which were added ten mGZL samples. Although we initially gathered 20 GZL, only the mediastinal were included in the study (n=14). Finally, we selected only the ten mGZL that successfully passed Quality Control. The signature produced a successful clustering of cHL or PMBCL cases in all the series analyzed from different technology platforms. Notably, the mGZL broke down into the two clusters, either cHL or PMBCL subtypes on a transcriptomic ground (Figure 1). Moreover, to assess the specificity of the signature in categorizing mGZL within the cHL/PMBCL spectrum, we tested it on ten Follicular Lymphoma samples which, as expected, segregated in a stand-alone subgroup. In conclusion, we provided a proof of concept of a NanoString-based gene signature enabling a transcriptomic stratification of mGZL, adding up to their morpho-phenotypical categorization. If validated on larger cohorts, our approach might prompt the design of a useful molecular assay easily transferable to routine clinical practice. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Cell-Free DNA for Genomic Analysis in Primary Mediastinal Large B-Cell Lymphoma.

High-throughput sequencing of cell-free DNA (cfDNA) has emerged as a promising noninvasive approach in lymphomas, being particularly useful when a biopsy specimen is not available for molecular analysis, as it frequently occurs in primary mediastinal large B-cell lymphoma (PMBL). We used cfDNA for genomic characterization in 20 PMBL patients by means of a custom NGS panel for gene mutations and low-pass whole-genome sequencing (WGS) for copy number analysis (CNA) in a real-life setting. Appropriate cfDNA to perform the analyses was obtained in 18/20 cases. The sensitivity of cfDNA to detect the mutations present in paired FFPE samples was 69% (95% CI: 60–78%). The mutational landscape found in cfDNA samples was highly consistent with that of the tissue, with the most frequently mutated genes being B2M (61%), SOCS1 (61%), GNA13 (44%), STAT6 (44%), NFKBIA (39%), ITPKB (33%), and NFKBIE (33%). Overall, we observed a 75% concordance to detect CNA gains/losses between DNA microarray and low-pass WGS. The sensitivity of low-pass WGS was remarkably higher for clonal CNA (18/20, 90%) compared to subclonal alterations identified by DNA microarray. No significant associations between cfDNA amount and tumor burden or outcome were found. cfDNA is an excellent alternative source for the accurate genetic characterization of PMBL cases.

Genomic and Transcriptional Characterization of Primary Mediastinal Large B Cell Lymphoma

Introduction: Primary mediastinal large B-cell lymphoma (PMBL) is a rare non-Hodgkin lymphoma subtype that occurs predominantly in young adults, with an overall favorable prognosis. The cell of origin is presumed to be thymic medullary B-cells and the gene expression profile of PMBL is similar to classic Hodgkin lymphoma. Recent studies have begun unravelling the genomic alterations underlying PMBL. Frequent, recurrent mutations (e.g. B2M, TNFAIP3, SOCS1, STAT6, GNA13) have been reported, but most of the studies have analyzed a small number of cases. To gain further insights into disease biology, we recruited 63 cases of PMBL as part of the Atlas of Blood Cancer Genomes (ABC-G) initiative, a consortium consisting of 25 institutions.Methods: Formalin-fixed paraffin-embedded (FFPE) biopsies and clinical data were collected. All cases were subjected to centralized review by an experienced panel of hematopathologists to ensure accurate diagnosis. Whole-exome DNA and RNA sequencing was performed using the Illumina platform and the DNA and RNA reads aligned to the GRCh38 genome and transcriptome respectively. Exonic variants were filtered using a set of paired normal samples and population-based databases to identify putative driver mutations, which were then aggregated at the gene level. Mutational analysis was performed on 56 samples that passed quality filtering and expression analysis on 45 samples. RNAseq data was normalized using DESeq2.Results: The cohort included samples from 16 males and 24 females, with a median age of 33 years (range 16 - 72) at the time of diagnosis. The majority of patients were treated with R-CHOP (47%) or R-EPOCH (43%), with 93% of patients surviving through the end of follow-up (median follow-up: 60.1 months). Besides the known recurrent mutations involving the JAK-STAT (STAT6 -21%, SOCS1 - 26%), NFKB (TNFAIP3 - 27%, NFKB1A - 7%), immune escape (B2M - 20%, LTB - 11%, IRF8 - 9%, IRF4 -9%), and chromatin modification (ZNF217 - 16%, CREBBP - 11%, KMT2D -11%) pathways , we discovered recurrent somatic variants in novel candidate driver genes in this disease, including NOTCH4 (7%), DICER1 (11%), MCL1 (7%), amongst others. EZH2, EP300, and XPO1 mutations were not detected. CIITA mutations and fusions were observed in 14% and 11% of cases, respectively, with novel partner genes (IGHA2, IGHG1, CDC6) detected in 67% of the fusion positive cases. Copy number alterations included gains at 2p16.1 (REL - 20%) and 9p24.2 (JAK2/PDL1/PDL2 - 24%), as well as loci not previously implicated in PMBL, 8q24.3 and 9q34.3 (each in 20%). Of note, CIITA alterations and 9p24 gains were virtually mutually exclusive, highlighting diverse mechanisms of immune escape in this entity. The transcriptomes of cases harboring CIITA alterations demonstrated differential enrichment of genes involved in protein glycosylation. The PMBLs in our series showed significant enrichment of the reported PMBL genetic classifier score, compared to nodal diffuse large B cell lymphoma (DLBCL) (p=0.0003). Finally, the gene expression profile of thymic B cells was more similar to that of PMBL than nodal DLBCL (p=0.0144).Conclusions: Our study, representing one of the largest comprehensive genomic and transcriptomic analyses of PMBL, expands the mutational landscape of PMBL, provides evidence for biologically distinct disease subsets and suggests an origin of PMBLs from thymic B-cells. DisclosuresHsi: AbbVie: Research Funding; Eli Lilly: Research Funding; Cytomx: Honoraria; Seattle Genetics: Honoraria. McKinney: BTG: Consultancy; Celgene: Consultancy, Research Funding; Epizyme: Consultancy; Genetech: Consultancy, Honoraria, Research Funding; Incyte: Research Funding; Kite/Gilead: Honoraria, Speakers Bureau; Molecular Templates: Consultancy, Research Funding; Nordic Nanovector: Research Funding; Novartis: Research Funding; Pharmacyclics: Consultancy; Verastem: Consultancy; Beigene: Research Funding; ADC Therapeutics: Consultancy, Speakers Bureau. Jaye: Stemline Therapeutics: Honoraria. Cohen: Genentech, Takeda, BMS/Celgene, BioInvent, LAM, Astra Zeneca, Novartis, Loxo/Lilly: Research Funding; Janssen, Adaptive, Aptitude Health, BeiGene, Cellectar, Adicet, Loxo/Lilly, AStra ZenecaKite/Gilead: Consultancy. Behdad: Lilly: Speakers Bureau; Roche/Foundation Medicine: Speakers Bureau; Thermo Fisher: Speakers Bureau. Dave: Data Driven Bioscience: Current equity holder in publicly-traded company.

Clinicopathological features and prognosis of primary mediastinal large B-cell lymphoma: a series of sixty cases

Objective: To investigate the clinicopathological features and prognostic factors of primary mediastinal large B-cell lymphoma (PMBL). Methods: The clinical data of 60 patients with PMBL including 44 biopsy cases and 16 consultation cases from September 2000 to November 2019 in the Department of Pathology, China-Japan Friendship Hospital (14 cases) and Peking Union Medical College Hospital (46 cases) were enrolled. Pathologic features, immunophenotype, immunoglobulin (Ig) gene rearrangement and microRNA expression profile were retrospectively studied. Results: Of the 60 patients, 23 were males and 37 were females, age ranged from 15 to 64 years (median 28 years). Immunohistochemical staining showed that the tumor cells were positive for pan-B cell antigens, CD30 (77.4%, 24/31), CD23 (73.1%, 19/26), MUM1 (45.8%, 11/24), Ki-67 index ≥70 % (90.6%, 29/32). EBER in situ hybridization was analyzed in 21 PMBL, only one case (4.8%) was positive. Ig gene rearrangement was performed in 20 cases, and seven were positive (35.0%). MicroRNA gene expression profiles were analyzed in seven cases of PMBL and nine cases of diffuse large B-cell lymphoma, and there were 33 microRNAs with significant difference (P<0.05). Univariate analysis indicated that the poor prognostic factors included serum lactate dehydrogenase (LDH) level,International Prognostic Index (IPI) score ≥3, stages Ⅲ-Ⅳ, chemotherapy not combined with rituximab and MUM1 positivity (P<0.05). Multivariate analysis showed that the treatment combined with rituximab was independently related to prognosis (P<0.05). Conclusions: PMBL is different from diffuse large B-cell lymphoma in clinicopathologic features, immunophenotypic presentation and molecular features. The prognostic factors, molecular genetics and immunological characteristics reveal that this study has enriched our understanding of the biology of PMBL, thus providing evidence and strategies for treatment.

Ruxolitinib shows activity against Hodgkin lymphoma but not primary mediastinal large B-cell lymphoma

BackgroundThe upregulated expression of the JAK/STAT pathway promotes tumor growth in Hodgkin lymphoma (HL) and primary mediastinal large B-cell lymphoma (PMBCL). Based on the hypothesis that JAK2 is a therapeutic target, we performed a prospective pilot study using ruxolitinib.MethodsRelapsed or refractory patients with HL or PMBCL were eligible for this study, and JAK2 amplification was assessed by fluorescence in situ hybridization. Ruxolitinib was administered orally at a dose of 20 mg twice daily for a 28-day cycle. Treatment was continued for up to 16 cycles or until progressive disease or intolerability. The primary objective was to assess the overall disease control rate comprising complete response (CR), partial response (PR), or stable disease (SD).ResultsWe analyzed 13 HL patients and six PMBCL patients. All responders (one CR, five PR, and one SD) had HL whereas all cases of PMBCL progressed after first or second cycle. The disease control rate for HL was 54% (7/13) with median response duration of 5.6 months. JAK2 amplification was present in six of nine patients tested (four HL, two PMBCL), and three of these HL patients showed PR (n = 2) or SD (n = 1). None of the three HL patients shown to not have JAK2 amplification responded to ruxolitinib. Most treatment-related adverse events were grade 1 or 2 and manageable.ConclusionsRuxolitinib has single-agent activity against HL but does not act against PMBCL with or without JAK2 amplification.Trial registrationThe study population was patients who had relapsed or refractory HL or PMBCL, and patients were registered for our pilot study after providing written informed consent between November 2013 and November 2015 (CilinicalTrials.gov: NCT01965119).

The utility of CD83, fascin and CD23 in the differential diagnosis of primary mediastinal large B-cell lymphoma versus classic Hodgkin lymphoma

Primary mediastinal large B-cell lymphoma (PMBL) and classic Hodgkin lymphoma (CHL) are the most common large cell lymphomas arising in the mediastinum and are thought to be closely related histogenetically. Although the distinction between PMBL and CHL is usually straightforward, in some cases it is challenging and rarely these neoplasms have intermediate features and qualify for the diagnosis of mediastinal gray zone lymphoma (GZL). CD83 and fascin are markers of CHL and CD23 is a marker of PMBL. In this study we assess the utility of this combination of these immunohistochemical markers to distinguish CHL from PMBL. We retrospectively collected cases of PMBL, CHL and GZL from three centers. Tissue sections were stained with CD83, fascin and CD23. CD83 was expressed in the neoplastic cells of 100% of CHL (22/22), 93% of GZL (16/18) and 41% of PMBL (9/22). Similarly, fascin was positive in the neoplastic cells of 100% of CHL (22/22), 86% of GZL (18/21) and 32% of PMBL (7/22). CD23 was positive in 95% of PMBL (21/22), 67% of GZL (12/18) and 9% of CHL (2/22). CD83 and fascin are sensitive markers for CHL but not specific whereas CD23 is sensitive for PMBL and uncommon in CHL. The GZL cases in this study had an intermediate immunophenotype, but the results were closer to CHL than PMBL. A large panel of immunohistochemical studies is recommended to distinguish CHL from PMBL entities and we suggest that CD83, fascin and CD23 add value to panels designed for this differential diagnosis.

Poor predictive value of positive interim FDG-PET/CT in primary mediastinal large B-cell lymphoma.

Though commonly used to assess response to therapy, the prognostic value of interim FDG-PET/CT in Primary Mediastinal Large B-cell Lymphoma (PMBCL) is unclear. We conducted a retrospective study on 36 consecutive patients treated at our institution for a PMBCL between 2006 and 2014. All patients with a positive interim FDG-PET/CT had undergone histological restaging consisting either in a surgical debulking of the residual lesion (15 patients) or a CT-guided core needle biopsy (two patients). All FDG-PET/CT were secondarily reviewed according to the more recent Deauville criteria. Interim FDG-PET/CT was considered positive in 17/36 patients using visual evaluation. Among these patients, 14 had a Deauville score of 4. Histological restaging was negative in all but one case, showing inflammation and/or fibrosis. After a median follow-up of 48.5months, a total of five patients have relapsed, two patients in the positive FDG-PET/CT group, and three patients in the negative FDG-PET/CT group, respectively. These data indicate that a positive interim FDG-PET/CT does not reflect persistence of active disease in the vast majority of PMBCL cases. The relapse rate appears similar regardless of interim FDG-PET/CT results and interpretation criteria. This suggests that interim FDG-PET/CT has a poor positive predictive value, thus kt should be used with caution in PMBCL.

Performance of a Commercially Available MAL Antibody in the Diagnosis of Primary Mediastinal Large B-Cell Lymphoma

Myelin and lymphocyte (MAL) protein has been previously reported as a highly specific marker for distinguishing primary mediastinal large B-cell lymphoma (PMBL) from diffuse large B-cell lymphoma, not otherwise specified (DLBCL, NOS). However, there has not been a commercially available MAL antibody for immunohistochemistry. We identified a commercially available MAL monoclonal antibody and evaluated it by immunohistochemistry on 43 cases of PMBL and 63 cases of DLBCL, NOS. We also compared this with a CD200 antibody that was previously reported useful in distinguishing PMBL and DLBCL, NOS. A threshold of 10% positive tumor cells was used to determine positive protein expression. MAL was expressed in 72% cases of PMBL and 0% of cases of DLBCL, NOS (sensitivity=72%, specificity=100%). CD200 was expressed in 81% of PMBL cases and 13% of DLBCL, NOS cases (sensitivity=81%, specificity=87%). To our knowledge, this is the first report on the utility of a commercially available MAL monoclonal antibody in the diagnosis of PMBL. There is a high specificity with good sensitivity in distinguishing PMBL from DLBCL, NOS, similar to previous studies with a noncommercial source. This antibody will likely prove useful in identifying cases of PMBL in routine practice.

Abstract 3941: Recurrent IL4R mutations in primary mediastinal large B cell lymphoma

Abstract Introduction: Primary mediastinal large B cell lymphoma (PMBCL) is a distinct subtype of aggressive B cell lymphoma that arises from thymic medullary B cells and characteristically presents as a mass in the anterior mediastinum. A proportion of PMBCL patients suffer from refractory or relapsing disease, and subsequent salvage therapies are frequently ineffective. Development of targeted therapies is impeded by the lack of knowledge about the mutational landscape in the lymphoma genomes and mutation-associated phenotypes. We recently reported somatic mutations in the transcriptome of 7 PMBCL patients and 3 cell lines by next-generation sequencing and found a hotspot mutation in exon 8 of IL4R (Gunawardana et al, Nat Genet, 2014). Interleukin (IL)-4 is a type II cytokine that regulates immune responses through binding to a receptor complex consisting of the IL4 receptor alpha (IL4Rα) chain and IL13Rα or the common gamma chain (γc). Activation of IL4R by IL-4 and/or IL-13 initiates intracellular signal transduction mediated by the phosphorylation of JAnus Kinase-Signal Transducer and Activation of Transcription (JAK-STAT) pathway. We hypothesize that constitutively active JAK-STAT observed in PMBCL is in part due to gain-of-function IL4R mutations signaling through this oncogenic pathway. Methods and samples: A sequencing cohort consisting of fresh-frozen pretreatment lymph node biopsies from 62 PMBCL cases were selected from the BCCA tissue archive. DNA from PMBCL tumors and 3 PMBCL-derived cell lines were extracted for IL4R exonic PCR amplification and Sanger sequencing or high-throughput sequencing on an Illumina MiSeq instrument. WT and mutant (I242N) IL4R cDNA were cloned into mammalian expression vectors and expressed in the lymphoma cell line DEV and in engineered HEK293 cells expressing STAT6. Supernatant from cultured cells were used to measure the activity of STAT6-dependent expression of secreted embryonic alkaline phosphatase (SEAP). Extracted RNA and protein from transfected cells were used for qRT-PCR and Western blotting, respectively. Results: Somatic IL4R mutations were found in 18 of 65 (28%) cases confirming a hotspot mutation (I242N) in exon 8 in 11 of 18 (61%) mutated cases. Ectopic expression of the mutant in HEK293 cells showed increased SEAP levels compared to WT (534% vs. 100%) indicating STAT6 activation independent of cytokine stimulation. Introduction of the mutant into DEV cells showed IL4 independent hyperphosphorylation of JAK2, STAT5 and STAT6 proteins and upregulation of the B cell activation marker CD23 (963% vs. 100% in WT). Conclusions: IL4R is frequently mutated in PMBCL with a recurrent hotspot affecting the transmembrane domain of the protein. Functional analyses characterize these mutations as gain-of-function leading to constitutive activation of the JAK-STAT pathway and downstream target genes. These data suggest IL4R mutations as novel driver alterations in PMBCL and may provide a rational therapeutic target. Citation Format: Jay Gunawardana, Tessa Van Tol, Katina Mak, David Twa, Elizabeth Chavez, Bruce Woolcock, Robert Kridel, Anja Mottok, Shannon Healy, Adele Telenius, Merrill Boyle, Susana Ben-Neriah, Stacy Hung, Christoffer Hother, Randy Gascoyne, Christian Steidl. Recurrent IL4R mutations in primary mediastinal large B cell lymphoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3941. doi:10.1158/1538-7445.AM2015-3941

Genetic Alterations of the MHC Class II Transactivator CIITA Are Frequent in Primary Mediastinal Large B-Cell Lymphoma and Associated with Diminished MHC Class II Expression

Introduction: Constitutive MHC class II expression is a hallmark of antigen-presenting cells, including B cells, and is indispensable for the initiation of antigen specific immune responses. It has been shown that certain B cell lymphoma entities are able to evade immune recognition by downregulation of MHC molecules on the tumor cell surface. We have previously identified recurrent chromosomal rearrangements of CIITA, the master regulator of MHC class II transcription, as one possible mechanism to reduce MHC class II expression in primary mediastinal large B-cell lymphoma (PMBCL) and classical Hodgkin lymphoma (cHL) (Steidl et al., Nature 2011). Furthermore, we have recently described a 1.6kb breakpoint cluster region within intron 1 of CIITA and have shown in a small sample set of PMBCL cases that deletions, insertions and single nucleotide variants (SNV) are commonly found within this genomic region (Steidl, ASH abstract # 437, 2011). Therefore, we aimed to explore the frequency of these alterations and the correlation with CIITA and MHC class II protein expression in a larger cohort of PMBCL cases and to further characterize their functional significance.Methods: We have comprehensively analyzed 45 diagnostic PMBCL samples for the presence of coding sequence mutations as well as alterations within the promoter III region and the first 3kb of intron 1 using deep amplicon sequencing (Illumina TruSeq) and/or Sanger sequencing. In addition, we characterized the PMBCL-derived cell lines U2940 and Med-B1 by whole transcriptome paired-end sequencing (RNA-seq). To elucidate the functional consequences of the coding sequence mutations identified in these two cell lines we performed retroviral transductions of wild type CIITA and CIITA mutants in a CIITA and HLA-DR expression-negative cell line (DEV, nodular lymphocyte predominant Hodgkin lymphoma-derived). We subsequently analyzed CIITA mRNA expression using qRT-PCR and HLA-DR surface expression using flow cytometry. Furthermore, we applied immunohistochemistry (IHC) to determine expression levels of CIITA and HLA-DR in a large cohort of PMBCL samples represented on two tissue microarrays (TMA, n=149). The TMAs were also used for fluorescence in-situ hybridization (FISH) to evaluate the presence of copy number alterations or translocations of the CIITA locus.Results: FISH was interpretable in 115 samples with a CIITA break-apart (CIITA-ba) frequency of 33.9% (39/115). Correlative analyses revealed that decreased CIITA protein expression by IHC was significantly correlated with the presence of CIITA-ba (P=0.019), whereas HLA-DR expression was not correlated with CIITA-ba status alone (P=0.219). However, we could demonstrate a positive correlation between protein expression of CIITA and HLA-DR (Pearson r=0.45, P<0.0001). Within the subset of 45 PMBCL cases that were analyzed for the presence of genomic alterations, 39% were CIITA-ba positive (16/41), and in 31.8% (14/44) we observed coding sequence mutations and/or alterations affecting the promoter III region. 45.5% (20/44) of the cases presented indels and/or SNVs in intron 1.Using RNA-seq, we have detected two missense mutations in the Med-B1 cell line affecting both alleles in functionally relevant protein domains. Furthermore, we identified a novel NUBP1-CIITA fusion transcript in U2940 also harboring an SNV on the other allele resulting in the transcription of an elongated protein due to the loss of the original stop codon. Ectopic expression of these CIITA mutants in DEV, which has been shown to have undetectable levels of CIITA and HLA-DR due to a biallelic CIITA inactivation, revealed that these individual SNVs showed a diminished capability to restore HLA-DR surface expression in comparison to wild type CIITA as measured by flow cytometry.Conclusions: Here we show that the presence of CIITA rearrangements is significantly associated with low CIITA protein levels, and we could demonstrate that protein expression of CIITA and HLA-DR are positively correlated in PMBCL. Furthermore, CIITA is frequently targeted by coding sequence mutations and intronic deletions in PMBCL cell lines and clinical samples. Functional studies demonstrate that genomic alterations in CIITA contribute to downregulation of MHC class II expression in malignant lymphomas and therefore represent a potent mechanism of acquired immune privilege and escape from immune surveillance. DisclosuresNo relevant conflicts of interest to declare.

Early CNS relapse in a good-risk primary mediastinal large B-cell lymphoma after combined chemo- and radio-therapy

CNS recurrence of non-Hodgkin lymphoma is fetal in most cases and tends to occur 5–12 months after the initial diagnosis [1]. Risk factors for CNS involvement include advanced stage, increased IPI, raised LDH, young age, [1 extranodal site, B symptoms, low albumin and retroperitoneal disease. A 19-year-old Japanese man presented to our hospital because of persistent cough on October 2007. A CT scan showed an anterior mediastinal tumor of 8 cm in diameter. LDH value and bone marrow examination were normal. After the total resection, the tumor was diagnosed as primary mediastinal large B-cell lymphoma (PMLBL). Involvement of right infraclavicular lymph nodes detected by Ga-SPECT and FDG-PET/CT determined the stage as IIA. One cycle of MACOP-B regime plus bi-weekly rituximab therapy started on November 2007. After confirming complete response (CR) by CT and Ga-SPECT, 30 Gy of involved field irradiation to the mediastinum and bilateral infraclavicular lymph nodes followed. On June 2008, 3 months after the chemoand radio-therapy, FDG-PET/CT revealed diminishment of abnormal accumulation. On July 2008, only 4 months after the completion of treatment, severe headache and nausea started. A cranial MRI scan showed an enhancing mass in the left frontal lobe with the right midline shift (Fig. 1). Although systemic evaluation revealed no recurrence in the other sites, brain biopsy confirmed infiltration of the lymphoma cells. Southern blot analysis of JH region of immunoglobulin heavy chain gene showed identical rearrangement bands in mediastinal tumor and CNS metastatic mass. The result confirmed that the CNS tumor is truly derived from primary mediastinal mass. The CNS lesion was resistant to two cycles of IVAM therapy containing high-dose methotrexate (MTX) and the following whole brain irradiation of 50 Gy. Then, after obtaining informed consent from the patient, we introduced via Ommaya reservoir three times of 10–25 mg of rituximab together with 3 ml of the autologous serum twice a week. The intracranial rituximab therapy failed to reduce the tumor size at least until day 15, when the patient’s condition rapidly deteriorated and subsequently he died of bacterial pneumonia. PMLBL is a relatively rare subtype of diffuse large B-cell lymphoma (DLBL) and usually occurs in young patients. MACOP-B regimen plus rituximab (R-MACOP-B) combined with local mediastinal radiation ([30 Gy) is recommended as a front-line therapy for the PMLBL patients [2]. This approach has demonstrated a stable progression-free survival in about 70% of the patients 2 years after the diagnosis. The presented patient was also treated with R-MACOP-B combined with involved field radiation and had no CNS risk factors except for young age, but he relapsed only 4 months after the completion of treatment. CNS relapse is reported in more than 10% of NHL arising from the testis, breast and paranasal sinuses, and CNS prophylaxis is recommended to these subtypes of DLBCL [3, 4]. Bishop et al. reported that CNS infiltration occurs in 4% of newly diagnosed PMLBL cases and in 11% of relapsed ones [5]. Although CNS recurrence has been reported in 2–10% of PMLBL patients [6–8], only one report has referred the CNS screening and prophylaxis in PMLBL [3]. Stefoni et al. reported a case of PMLBL M. Sasaki (&) K. Sugimoto A. Masuda Y. Tsukune Y. Yahata N. Komatsu Division of Hematology, Department of Internal Medicine, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan e-mail: msasaki@juntendo.ac.jp

Differential JAK-STAT Pathway Activation in Primary Mediastinal Large B-Cell Lymphoma: Two Subgroups with Differential Cytokine Activation Patterns and Predicted Responses to Kinase Inhibitors.

Abstract 968 Background:Primary mediastinal large B-cell lymphoma (PMBCL) is a specialized type of diffuse large B-cell lymphoma which shows diagnostic and pathogenetic overlap with mediastinal classical Hodgkin lymphoma. Approximately 60% of patients with PMBCL have good response to conventional chemoradiotherapy with the rest often showing distant relapses. Microarray studies of PMBCL have revealed overexpression of components and targets of the JAK-STAT signaling pathways including upregulation of IL13 receptor and STAT1; a subset of PMBCL have genome amplification of JAK2 or deletion of the JAK suppressor SOCS1. Given this complexity, we examined the most common mechanism and effects of JAK-STAT dysregulation in a series of newly diagnosed and recurrent PMBCL. Methods:Fifty-three biopsies from 23 patients with PMBCL were assessed and correlated with outcome. JAK2 and SOCS1 copy number status were determined by quantitative PCR on genomic DNA. JAK-STAT pathway activation was probed using reverse transcription quantitative (RQ)-PCR for JAK2, JAK3, and a panel of IL-4 and IL-13 transcriptional targets. JAK-STAT activation was assessed in tissue arrays using antisera against phospho-activation epitopes of STAT1, STAT3, STAT5, and STAT6 using immunohistochemistry (IHC). Activation patterns were modeled in the PMBCL cell line Karpas (K)1106P at baseline and following IL-4 and IL-13 stimulation with or without a range of small molecule inhibitors and blocking antibodies. Growth parameters were measured by MTT and protein levels by flow cytometry, Western blot, RQ-PCR and kinase profiling. Results:JAK2 genomic amplification was present in 40% of PMBCL and SOCS1 deletion in 10% as well as in the K1106P line. By phospho-activation IHC, tumors in 20/23 (87%) patients showed STAT activation, mostly due to STAT1 (60.8%) followed by STAT3 (26.1%), with 6 cases showing mixed patterns. In different tumors, localized and uniform STAT activation patterns were seen. Constitutive STAT activation was correlated with high expression of IL-4 transcription targets including CCL17 and IL13RA as well as JAK2 autophosphorylation and inferior outcome (p = .007). Tumors with more localized foci of activation were associated with alternate transcription patterns. In the K1106P cell line, IL-4 but not IL-13 treatment led to inducible STAT1 activation whereas baseline STAT3/6 activation was highly regulated by cytokine exposure. The JAK2 inhibitor JSI124 blocked IL-4 induced STAT1 activation whereas the JAK inhibitors AG-490, NSC7908 and WHI-P154 did not but did block IL-4/IL-13-induced STAT3 activation. The JAK3 inhibitor ZM39923 was most effective in blocking cell growth but did not block STAT1 activation. Conclusions:JAK2-STAT pathway activation characterizes nearly all cases of PMBCL but genetic mechanisms are distinct leading to distinct patterns of STAT1 activation (driven predominantly through the type I IL-4 receptor) and STAT3/6 activation (driven predominantly through the type II IL13RA/IL4RA) with differential effects on growth parameters and gene regulation. The patterns of STAT activation and target gene expression in primary tumors comprising these two groups mirrored the response to small molecule inhibitors following cytokine exposure in vitro in the K1106P line and highlights differences between IL-4 and IL-13 signaling in PMBCL. Profiling of PMBCL biopsies with phosphoactivation IHC for STAT isoforms may be useful to subcategorize cases and select the optimal JAK-STAT pathway inhibitors for adjuvant therapy. Disclosures:No relevant conflicts of interest to declare.

Primary mediastinal B-cell lymphoma: detection of BCL2 gene rearrangements by PCR analysis and FISH

Primary mediastinal large B-cell lymphoma (PMBCL) has a characteristic clinical presentation, morphology, and immunophenotype, representing a clinically favorable subgroup of diffuse large B-cell lymphoma (DLBCL). By gene expression profiling (GEP), PMBCL shares features with classical Hodgkin lymphoma (cHL). Of further interest, BCL6 gene mutations and BCL6 and/or MUM1 expression in a number of PMBCLs have supported an activated B-cell (ABC) origin. Several studies, including GEP, have failed to detect BCL2 gene rearrangements (GRs) in PMBCL. An index case of t(14; 18)+ PMBCL prompted our study of the incidence of BCL2 GRs in PMBCL by polymerase chain reaction (PCR)/fluorescence in situ hybridization (FISH) analyses and its possible clinical impact. Twenty-five retrospectively identified, well-defined PMBCLs (five with cytogenetics) from three institutions were analyzed for a BCL2 GR by PCR/FISH analyses. The formalin-fixed, paraffin-embedded tissue blocks of 24 available cases were also analyzed by BCL2 immunohistochemistry (IHC). Of the five with cytogenetics, two had a t(14; 18) (q32; q21). Of the 25 analyzed by PCR, 2 had no amplifiable DNA (aDNA), including 1 t(14; 18)+ case. Of those with aDNA, two showed a BCL2 GR; by FISH analysis, three demonstrated a BCL2 GR. BCL2 protein expression by IHC analysis was variably detected in 21 out of 24 (strongly, uniformly expressed: 6, including all with a t(14; 18) or a BCL2 gene rearrangement; moderately weakly expressed in a subset of the malignant cells: 15). Available clinical follow-up of this BCL2+ subset showed a similar course to the other PMBCL cases. Our results imply that a subset of PMBCL [(4 out of 24 analyzed) in our series] may be of GC origin. A larger study is necessary to determine any clinical significance.

Expression of TRAF1 and Nuclear c-Rel Distinguishes Primary Mediastinal Large Cell Lymphoma From Other Types of Diffuse Large B-cell Lymphoma

Primary mediastinal large B-cell lymphoma (PMLBCL) is a recently identified subtype of diffuse large B-cell lymphoma (DLBCL) that is difficult to distinguish from other types of DLBCL on the basis of histologic features alone. We recently identified a molecular signature of PMLBCL that is distinct from other forms of DLBCL but shares features with classical Hodgkin lymphoma. This signature includes activation of the nuclear factor kappaB (NFkappaB) signaling pathway, which in part, acts through nuclear translocation of c-Rel containing NFkappaB transcriptional complexes, and subsequent expression of NFkappaB target genes such as tumor necrosis factor receptor-associated factor-1 (TRAF1). Using standard immunohistochemical techniques, we examined 251 large B-cell lymphomas (78 cases of PMLBCL and 173 cases of other types of DLBCL) to determine whether the expression patterns of c-Rel and TRAF1 could reliably distinguish between PMLBCL and other types of DLBCL. Robust nuclear c-Rel was present in 31 of 48 (65%) cases of PMLBCL and 28 of 160 (18%) cases of DLBCL. In addition, cytoplasmic TRAF1 expression was seen in 48 of 78 (62%) cases of PMLBCL, but only 20 of 173 (12%) cases of DLBCL. Finally, the combined expression of nuclear c-Rel and TRAF1 was seen in 24 of 45 cases (53%) of PMLBCL, but in only 3 of 156 cases (2%) of other types of DLBCL. Thus, the combined nuclear localization of c-Rel and the cellular expression of TRAF1 is a highly specific (specificity=98%) means to distinguish PMLBCL from DLBCL that is readily applicable to routine surgical pathology practice.