1. R4 고원진 / 백선경 교수님 JOURNAL OF CLINICAL ONCOLOGY Volume 29, Number 14, May 2011 The Gray Zone Between Burkitt’s Lymphoma And Diffuse Large B-Cell Lymphoma From a Genetics Perspective Itziar Salaverria and Reiner Siebert

2. The border between Burkitt’s lymphoma(BL) and diffuse large B-cell lymphoma [DLBCL] : Uncertainty BL and DLBCL : Both extremes of a continuum of mature aggressive B-cell lymphoma The updated WHO classification : Aggressive B-cell lymphomas “that have morphological and genetic features of both DLBCL and BL, but for biologic and clinical reasons should not be included in these categories”  B-cell lymphoma, unclassifiable, with features intermediate between DLBCL and BL INTRODUCTION

3. Compare the features of BL and DLBCL, to clarify the different definitions of intermediate lymphomas Describe subgroups in the gray zone between classical BL and DLBCL Purpose

4. Morphology : medium-sized cells and a diffuse monotonous pattern of growth The classical immunophenotype : IGM+/CD10+/BCL2-/BCL6+ and TdT- with the Ki-67 proliferation index higher than 95% The chromosomal translocation : t(8;14)(q24;q32) or t(8;22) or t(2;8) is present but not exclusive to this disease IG-MYC fusions result in deregulated expression of the intact MYC oncogene (SPORADIC) BL

5. In BL, IG-MYC fusion mostly is part of a simple karyotype, with secondary aberrations being singular events On the cytogenetic level : 70% of BL have no or only one secondary alteration Using 2.8K array comparative genomic hybridization(CGH) : –The most recurrent secondary changes are gains in 1q,7,12, and 13q, and losses of 6q,13q, and 17p –Whereas 17p deletions are supposed to affect the TP53 gene, the target genes of the other alterations are not yet known –Gains or amplifications of 1q and gains in 7q and an increasing genetic complexity have been reported to be associated with a poor clinical outcome A gene-expression profiling (GEP) : –Independent groups have been able to recognize specific gene expression signatures for BL that identify almost the very same lymphomas –The cases that carry this signature are described as molecular BL (mBL) and can be clearly differentiated from non-mBL

6. A group of morphologically, immunohistochemically, and clinically heterogeneous tumors rather than one single entity large B-cell lymphoid cells with big nuclei and a diffuse growth pattern Partial nodal involvement may be interfollicular and/or less commonly sinusoidal Morphologically, centroblastic, immunoblastic, and anaplastic variants : with the immunoblastic variant associated with inferior outcome The neoplastic cells express CD19, CD20, CD22, and CD79 Biologic subgroups : - favorable prognosis (germinal center B-cell like [GCB]) - poor prognosis (activated B-cell like [ABC]) In part, by immunohistochemistry using markers like CD10, BCL6, and MUM1/IRF4 DLBCL

7. Chromosomal translocations : –3q27, BCL6 gene, are one of the most common genetic abnormalities –the BCL2 gene through t(14;18)(q32;q21) : a hallmark of follicular lymphoma, is detected in 30% to 45% of GCB-DLBCL –MYC break in up to10% of patients with classical DLBCL and has been linked to complex karyotypes and a very unfavorable outcome –TP53 mutations : associated with poor survival

8. Aberrant hypermutation may represent a major contributor to lymphoma genesis of DLBCL –Somatic hypermutations of several genes like BCL6, PIM1, MYC, RhoH/TTF, and PAX5 –several of the hypermutable genes are also susceptible to chromosomal translocations –Ongoing IGHV somatic hypermutation has been more frequently described in GCB-DLBCL –Whereas ABC-type has abnormalities in the regulation of the immunoglobulin class switch recombination

9. The number of chromosomal imbalances in DLBCL is significantly higher than in BL Using 2.8K array CGH, –The molecular subgroups of DLBCL clearly show diverse patterns of chromosomal imbalances: GCB-DLBCL presents frequent gains of 2p, 12q, and 13q, as well as deletion in 10q whereas ABC-DLBCL carries more frequent gains/amplifications of 3/3q, 18q21-q22, and 19q, and losses of 6q21-q22 and 9p21

10. LYMPHOMAS INTERMEDIATE BETWEEN DLBCL AND BL: NONSYNONYMOUS DEFINITIONS BASED ON GENE EXPRESSION AND WHO CLASSIFICATION

11. The WHO 2008 classification affirms that the following lymphomas should not be regarded as intermediate BL/DLBCL : –typical DLBCL with a MYC translocation –typical BL in which a MYC rearrangement cannot be demonstrated –those with IG-MYC rearrangement as the only abnormality, since they probably correspond to real BL with atypical morphology POTENTIAL GRAY-ZONE BL AND DLBCL NOT CLASSIFIED AS INTERMEDIATE BL/DLBCL BY THE WHO CLASSIFICATION

12. The Gray Zone Between BL and DLBCL: Recognizable Subentities?

13. No impact on therapy decision or outcome in children MYC-positive lymphomas with intermediate gene expression in children mostly carry an IG-MYC fusion Intermediate lymphomas in children show a higher Burkitt index than adult patients Morphologic DLBCL in children show a GEP of mBL, These findings suggest that in childhood biologic BL might be hidden in the group of DLBCL Pediatric Lymphoma in the Gray Zone

14. Pediatric IG-MYC–positive mature aggressive B-cell lymphomas –the IG MYC fusion is the primary genetic event –Complex IG-MYC karyotypes most likely derive from a clonal evolution of an IG-MYC simple –Complex karyotypes can indicate disease progression associated with inferior prognosis Pediatric IG-MYC–negative mature aggressive B-cell lymphomas –unknown primary genetic lesion(s) –some evidence that also pediatric follicular lymphoma grade 3 –Morphologically, the group might contain primary mediastinal large B-cell lymphomas

15. The clinical impact of subgrouping lymphomas in the gray zone between BL and DLBCL currently seems to change with age the proper subclassification of mature aggressive B-cell lymphomas in adults might in future influence treatment decisions and prognosis of the patients Adult Lymphoma in the Gray Zone

16. Mature aggressive B-cell lymphomas with typical morphology, immunophenotype, and probably an mBL gene-expression pattern, which lack an identifiable MYC rearrangement –The major challenge is to distinguish technical failures in detecting an IG-MYC fusion from true MYC negative BL –The advent of next-generation sequencing of whole genomes will probably show whether MYC negative true BL exists at all –If we consider that all cases described as MYC-negative are true BL, there is evidence that these cases could present molecular peculiarities –IG-MYC–negative mBL defined only by GEP mostly lacks classical BL morphology and/or immunophenotype and shows a significantly higher number of chromosomal imbalances than IG MYC– positive mBL Adult MYC-negative mature aggressive B-cell lymphomas with Burkitt morphology and phenotype

17. Inferior prognosis with at least some of the currently applied treatment protocols Adult MYC–positive mature aggressive B-cell lymphomas lacking typical Burkitt morphology and phenotype

18. Genetically resemble BL, with IG-MYC translocation as primary event However, they present discrepancies from BL in terms of morphology and immunophenotype The define a “simple” karyotype : presence of a BCL2 or BCL6 translocation or another more rare but nevertheless classical primary oncogene translocation would render the definition of a karyotype “complex.” The definition of complexity : –recent high-resolution array-based approaches have mainly confirmed the highly conserved pattern of chromosomal imbalances –In this context, copy number variations present also in the germline should not be taken into account to define complexity Thus, a future direction could be to create bioinformatic algorithms that reliably distinguish a simple (BL) from a complex (DLBCL) karyotype IG-MYC–positive mature aggressive B-cell lymphomas with simple karyotype lacking typical Burkitt morphology and/or phenotype

19. These cases in addition to IG-MYC translocations carry a high genetic complexity whereas the definition of “genetic complexity” depends on resolution of the technique applied These cases can correspond either to evolution from BL (with a primary IG-MYC translocation) or to progression from DLBCL (with secondary acquisition of IG-MYC) Helpful features that allow the distinction between the two possible diagnoses are morphology, immunophenotype, and, particularly, age and localization of the tumor IG-MYC–positive mature aggressive B-cell lymphomas with complex karyotype lacking typical Burkitt morphology and/or phenotype

20. A steadily increasing number of MYC translocations involving other partners than IG regions –Non-IG-MYC translocations These cases could correspond to DLBCL that presents a primary genetic event like BCL2 or BCL6 translocation or other primary imbalances and secondary transformation During this transformation, they could acquire the non-IG- MYC translocation and latter develop the extremely genetically complex karyotypes observed frequently in transformed tumors Non-IG-MYC–positive mature aggressive B-cell lymphomas

21. Lymphomas with a MYC translocation and a second oncogene translocation are often referred to as “doublehit” lymphomas these lymphomas have a BCL2, BCL6, and/or CCND1 translocation as primary events with additional secondary MYC breakpoints The relative incidence of double- and triple-hit lymphomas increases with Age Clinically, these cases show a frequent involvement of the bone marrow, blood, and CNS Most cases are resistant to current therapies, which seem to be independent of the complexity of the other cytogenetic abnormalities Double-hit–positive mature aggressive B-cell lymphomas

23. Genetic aberrations are the key initiating events of lymphoma genesis and are associated with morphologic and immunologic features of tumor cells There is considerable evidence that many lymphomas in the gray zone between BL and DLBCL are associated with a poor outcome Whether this relates to the underlying biology or is due to suboptimal treatment assignment needs further investigation SUMMARY