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Primary mediastinal (thymic) large B-cell lymphoma (PMBL) is described as almost always negative for Epstein-Barr virus (EBV). In the context of a mediastinal lymphoma, the distinction between PMBL, classical Hodgkin lymphoma, diffuse large B-cell lymphoma, and mediastinal gray-zone lymphoma can be very difficult; hence, EBV positivity often argues against PMBL. We present a 19-year-old man with mediastinal mass morphologically consistent with PMBL. The tumor expressed classic immunophenotype, including positivity for CD20, CD19, MAL, OCT2, BOB1, BCL6, CD79a, and subset positivity for CD30. However, the tumor was EBV-positive by in situ hybridization. Next-generation sequencing detected somatic mutations in XPO1 (E571K), SMARCB1 (L356fs), and MYCC (T73A). Although the immunophenotype and XPO1 mutation are characteristic of PMBL, EBV expression is uncommon. Since EBV positivity can occur in rare PMBLs, it should not be the deciding factor in the diagnosis. This is the first EBV-positive PMBL in which mutational profiling has been reported. Aside from providing diagnostic support, the finding of the XPO1 E571K mutation may suggest a targeted therapeutic option.

Background Primary mediastinal (thymic) large B-cell lymphoma (PMBL) is described to be almost always negative for EBV in the current WHO. In the context of a mediastinal lymphoma, the distinction between PMBL, classic Hodgkin lymphoma (CHL), diffuse large B-cell lymphoma, and mediastinal gray-zone lymphoma can be very difficult; hence, EBV positivity often aids in pointing away from a diagnosis of PMBL. However, since EBV positivity can occur in rare PMBLs, it should not be the deciding factor in the diagnosis; assistance from molecular studies is emerging in these difficult cases. Case Presentation We present a 19-year-old male patient with a 2-week history of cough, vocal changes, and occasional dysphagia who was found upon imaging to have a 6-cm mediastinal mass. The biopsy of this mass was morphologically consistent with PMBL but the tumor was EBV positive by in situ hybridization. Methods We performed next-generation sequencing using Oncomine Comprehensive Assay v3 (ThermoFisher Scientific) on formalin-fixed, paraffin-embedded tumor tissue with a buccal swab sample for germline control. Variant calling, filtering, and annotation were performed by the Yale Tumor Profiling Laboratory. Results We found somatic mutations in XPO1, SMARCB1, and MYC. Along with classic immunophenotype of PMBL including positivity for MAL, OCT2, BOB1, BCL6, CD79a, MUM1, CD20, and subset weak CD30, the diagnosis was confirmed to be PMBL. Conclusion This is the first EBV-positive PMBL in which molecular profiling was performed. XPO1, specifically the mutation hotspot (E571K), found in our case is involved in PMBL and CHL. This was clinically helpful in confirming the histopathologic diagnosis and also opening up a targeted therapeutic option. Selective inhibitors of nuclear export (SINEs) that block the binding of XPO1 to its cargo are in clinical development as antineoplastic agents and have shown promising activity against some hematologic malignancies.

Pearson marrow pancreas syndrome (PS) is a multisystem disorder caused by mitochondrial DNA (mtDNA) deletions. Diamond-Blackfan anemia (DBA) is a congenital hypoproliferative anemia in which mutations in ribosomal protein genes and GATA1 have been implicated. Both syndromes share several features including early onset of severe anemia, variable nonhematologic manifestations, sporadic genetic occurrence, and occasional spontaneous hematologic improvement. Because of the overlapping features and relative rarity of PS, we hypothesized that some patients in whom the leading clinical diagnosis is DBA actually have PS. Here, we evaluated patient DNA samples submitted for DBA genetic studies and found that 8 (4.6%) of 173 genetically uncharacterized patients contained large mtDNA deletions. Only 2 (25%) of the patients had been diagnosed with PS on clinical grounds subsequent to sample submission. We conclude that PS can be overlooked, and that mtDNA deletion testing should be performed in the diagnostic evaluation of patients with congenital anemia.

Microangiopathic disorders present with thrombocytopenia, hemolytic anemia, and multiorgan damage. In pregnancy, these disorders present a challenge both diagnostically and therapeutically, with widely overlapping clinical scenarios and disparate treatments. Although rare, a clear understanding of these diseases is important because devastating maternal and fetal outcomes may ensue if there is misdiagnosis and improper treatment. Microangiopathic disorders presenting in pregnancy are thus best assessed and treated by both obstetric and hematology teams. As a better understanding of the pathophysiology underlying each of the disease processes is gained, new diagnostic testing and therapies will be available, which will lead to improved outcomes.

Klippel-Trenaunay Syndrome (KTS) is a rare, sporadic triad of congenital malformations involving an extensive port wine stain, soft tissue or bone hypertrophy and underlying venous and/or lymphatic malformation involving an extremity. Pregnancy is known to exacerbate KTS complications and can put women at increased obstetrical risk due to deep venous thrombosis and other thromboembolic events. Here we report a case of a patient with KTS who achieved a pregnancy through in vitro fertilization (IVF) using her own eggs and a gestational surrogate in the setting of hypercoagulability and chronic consumptive coagulopathy.

Pearson marrow pancreas syndrome (PS) is a congenital multisystem disorder characterized by sideroblastic anemia, pancreatic insufficiency, metabolic acidosis, and other defects, and is caused by mitochondrial DNA (mtDNA) deletions. Diamond Blackfan anemia (DBA) is a congenital hypoproliferative anemia with associated physical malformations, and in which mutations in ribosomal protein (RP) genes and GATA1 have been implicated. The clinical presentation of both of these bone marrow failure (BMF) syndromes shares several features including early onset of severe anemia, sporadic genetic inheritance, variable penetrance and manifestations, and episodes of spontaneous hematologic improvement. PS is less frequently occurring than DBA, with estimated incidences of < 1/1,000,000 versus 1/100,000 respectively, and therefore less often encountered by hematologists. We hypothesized that some patients in whom the leading clinical diagnosis is DBA actually have PS. To test this hypothesis, we retrospectively evaluated DNA samples from a cohort of patients that were submitted to a research study for DBA genetic testing. The study cohort consists of clinical samples and/or data from 362 patients, with a primary inclusion criterion of known or suspected congenital anemia. Prior genetic studies from this cohort have yielded the novel identification or confirmation of mutations and deletions in several genes implicated in DBA (e.g. RP genes, GATA1), which are to date identifiable in 175/362 samples (48%), a proportion consistent with that found in independent DBA registries. We screened peripheral blood DNA samples available from 173 genetically uncharacterized patients using a long PCR strategy, and found that 8 samples (4.6%) contained large mtDNA deletions. Deletion mapping and Southern blot analysis on DNA from these 8 patients confirmed the presence of a single deletion event within each patient, ranging in size from 2.3 - 7.0 kb of the 16.6 kb mitochondrial genome, existing as monomer or multimer mtDNA species, and in a proportion ranging from 55-80% of total mtDNA, all of which are consistent with the molecular diagnosis of PS. Follow-up with referring providers in the 1 month to 8 year time span since sample submission revealed that 2 of the 8 patients (25%) were subsequently diagnosed with PS. Of the remaining 6 undiagnosed patients, 2 had died from complications of bone marrow transplantation, performed for worsening cytopenias and concern for myelodysplasia; one patient died from bacterial sepsis; and 3 were alive with the provisional diagnosis of DBA. One of the 3 patients had become transfusion-independent. Review of bone marrow examinations revealed that the pathological hallmarks of ringed sideroblasts and/or vacuolization of precursors described in PS were inconsistently present or reported in the diagnostic evaluation. We conclude that PS is frequently overlooked in the diagnostic evaluation of children with congenital anemia. Establishing the diagnosis of PS, as distinct from DBA and other BMF disorders, holds important implications for patient management and family counseling. mtDNA deletion testing should be performed in the initial genetic evaluation of all patients with congenital anemia. Disclosures: Szczepanski: Octapharma AG: Investigator Other.

Abstract 683 The pathogenic mechanism of immune thrombocytopenia involves antibody mediated destruction of platelets in the reticuloendothelial system. Infection often triggers an exacerbation of thrombocytopenia in patients with ITP that may be treated with intravenous immunoglobulin (IVIG). However, the precise mechanism of action of IVIG has not been clearly elucidated. Studies by McKenzie et al. (Journal of Immunology, 1999) in an animal model for immune thrombocytopenia (ITP) using a mouse transgenic for human activating receptor FcgammaRIIA and lacking murine activating receptors FcgammaRI and FcgammaRIII revealed that human FcgammaRIIA is necessary for antibody mediated platelet destruction. (Murine macrophages lack an analogous activating FcgammaRII.) In another animal model of ITP, Samuelsson et al. (Science, 2001) showed that decreased expression of the murine inhibiting FcgammaRIIb was associated with increased platelet destruction that was not responsive to IVIG. The present studies were undertaken to test the hypothesis that human antibody mediated platelet phagocytosis depends upon the balance between the activating (FcgammaRIIA) and inhibiting (FcgammaRIIB) receptors on human macrophages and that IVIG alters this balance by increasing the expression of the inhibiting receptor. We additionally hypothesized that infection results in decreased FcgammaRIIB expression and enhanced phagocytosis that may be abrogated by IVIG. Methods: Antibody-mediated phagocytosis of platelets by THP-1 (human macrophage) cells in culture was assayed by co-incubation of THP-1 cells with anti-platelet antibody as a model for human immune mediated platelet destruction. Platelets were labeled with 5-(and 6-) carboxyfluorescein diacetate mixed isomers (CFDA) in the presence of human serum containing anti-HPA 1a IgG antibody. Macrophages that had ingested human platelets were identified by flow cytometry as previously reported. To study the mechanism of action of IVIG therapy for immune thrombocytopenia, in vitro phagocytosis was assayed after the addition of purified IgG (100mg/ml) to the THP-1 cells 30 minutes prior to exposure of the labeled platelets to anti-HPA 1a IgG antibody. The effect of LPS on platelet phagocytosis was studied as a model for infection which can exacerbate immune platelet destruction. Phagocytosis was assayed before and after incubation with LPS (1ug/ml) for 2 hours at 37 degrees Celsius. For each experiment, total FcgammaRIIA (CD32A) and FcgammaRIIB (CD32B) were determined by immunoprecipitation and immunoblotting. Results: Pretreatment with IVIG had no effect on FcgammaRIIA (n=3) expression; however, FcgammaRIIB expression increased an average of 5 fold (n=6). Addition of LPS alone resulted in marked decrease in expression of FcgammaRIIB for up to 60 minutes; however, FcgammaRIIA did not change. Experiments performed with addition of both IVIG and LPS showed that FcgammaRIIB expression remained elevated 3 fold (n=3). Following increased expression of FcgammaRIIB, IgG exposure resulted in decreased phagocytosis as assayed by flow cytometric analysis of macrophage ingestion of CFDA-labeled platelets. Antibody mediated platelet phagocytosis by THP-1 cells was enhanced 26% by LPS after a 2 hour incubation (median increase in 5 experiments; range = 14-125%.) Conclusions: Exposure to high dose IgG increased the expression of FcgammaRIIB but had no effect on FcgammaRIIA. Therefore, the net functional effect was to tip the balance toward inhibition of antibody-mediated phagocytosis, as was observed in our in vitro assay of human platelet phagocytosis. Furthermore, treatment with IgG was able to partially overcome the negative effects of LPS on expression of the inhibiting receptor, FcgammaRIIB. These data clearly support the hypothesis that the balance of the activating (FcgammaRIIA) and inhibiting (FcgammaRIIB) receptors is important in mediating the therapeutic effects of IVIG as a treatment for human immune thrombocytopenia. Disclosures: Pels: National Hemophilia Foundation-Baxter: NHF-Baxter Clinical Fellowship Awardee, Research Funding. Beardsley:ITP Foundation: Membership on an entity's Board of Directors or advisory committees; Genzyme: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees.