Early lesions of follicular lymphoma: a genetic perspective

Abstract

© F e r r a t a S t o r t i F o u n d a t i o nposed to distinguish FLIS from partial involvement by FL (PFL). In PFL there is greater architectural distortion, and the diagnosis of lymphoma is more evident histologically. However, interestingly, patients with PFL appear to present with low-stage disease, with a relatively low risk of progression and often a very prolonged disease-free interval with limited therapy. 12 Thus, PFL may represent a bona fide early stage in the biological evolution of FL, and not just a limited state of lymph node replacement by a fully developed neoplasm.14 Advances in laser capture microdissection now enable the isolation of even small numbers of cells representative of the clonotypic population, 15 and improvements in genomic methods allow the analysis of genetic aberrations in DNA derived from formalin-fixed, paraffin-embedded tissues. These new technologies now provide the unique opportunity to explore the genetic landscape of these early lesions, and to understand their relationship to overt FL better. Methods SamplesMost cases were selected from formalin-fixed, paraffin-embedded archive specimens submitted to the Hematopathology Section at the National Cancer Institute (NCI) or the Institute of Pathology, at the Medical University of Vienna. Seven cases of FLIS, five cases of PFL and five cases of DFL were identified based on previously published criteria. 11,12 Patients with FLIS and PFL had no other evidence of disease during the period of follow-up. 12 These samples were compared to five cases of FL grade 1-2 and five of FL grade 3A, included as controls of the most frequent alterations occurring in FL. Finally, sections of reactive follicular hyperplasia (RFH, n=2) and laser micro-dissected lymphoid cells from uninvolved areas of FLIS#3 (FLIS background) were also hybridized and used as references for normal cells (Online Supplementary Table S1). Only cases with confirmed t(14;18) were included in the study. The Institutional Review Boards of the NCI and the Medical University of Vienna approved the study. Laser capture microdissection, DNA extraction and quality controlTo obtain sufficient enrichment of lesional cells positive for t(14;18), which was necessary for the genome-wide array analysis, BCL2 + GC were microdissected from the selected FLIS/PFL/DFL/FL grade 1-2 cases. Laser capture microdissection was performed using a Leica LMD6000 (Leica Microsystems, Germany) on hematoxylin-stained slides with BCL2 + immunostained slides as a guide for involved follicles.15 BCL2-negative GC were microdissected from RFH, without evidence of FLIS. Tumor cell DNA was isolated from FL grade 3A without microdissection, given the high tumor cell content (>75%). DNA was extracted using a QIAamp ® DNA FFPE Kit. The amount of DNA collected from the different cases ranged from 506 to 2820 ng. With a calculation of 6.6 pg of DNA/cell this amounts to a minimum of 77,000 cells per case needed for appropriate hybridization. The integrity of the DNA was controlled with an Agilent DNA1...

Early lymphoid lesions: conceptual, diagnostic and clinical challenges

“…Two recent high-resolution array CGH studies of FLIS/FLBUS identified a paucity of genetic aberrations in comparison with FL, supporting the conclusion that these lesions are at a very early stage of evolution, and do not represent merely seeding of germinal centers by lymphoma at a distant site. 42,43 Of note, evidence for EZH2 mutations, thought to occur early in follicular lymphomagenesis, were found in both reports. Duodenal follicular lymphoma (DFL) showed a similar low level of aberrations, while PFL appeared to represent an intermediate stage of evolution.…”

“…50 High resolution array CGH analysis has shown that DFL shares genomic aberrations with FLIS and PFL suggesting common pathways of origin. 42 However, unlike in PFL, a large fraction of these alterations were not shared with FL. In the context of reduced AID expression in DFL, these aberrations could have occurred before downregulation of AID or independent of it.…”

“…Duodenal follicular lymphoma (DFL) showed a similar low level of aberrations, while PFL appeared to represent an intermediate stage of evolution. 42 The specific factors that determine progression of FLIS/FLBUS to FL still have to be clarified, but if there is no other evidence of disease at diagnosis, the risk of progression is low (less than 10%). 36 However, analogous to MGUS and MBL, retrospective review of "reactive" lymph nodes biopsied prior to a FL diagnosis has shown FLIS/FLBUS in a subset.…”

Lymphome folliculaire

“…Pour répondre à cette question, nous avons créé un modèle murin dont l'objectif était de récapituler le plus fidèlement possible les étapes précoces de progression du lymphome folliculaire, depuis l'expression sporadique de la translocation t(14;18) chez l'individu sain (dans ~ 1 cellule sur 1 million) jusqu'aux formes les plus pré-coces, telles que le « lymphome folliculaire in situ » (FLIS). Le FLIS est considéré comme l'entité clinique la plus précoce du lymphome folliculaire ; celle-ci se manifeste par une colonisation partielle des centres germinatifs (en général quelques foci BCL2 + au sein de centres germinatifs normaux par ailleurs, BCL2 -, sans distorsion architecturale), et progressant vers un lymphome folliculaire dans ~ 5 % des cas [9]. Dans notre modèle nommé un marqueur spécifique de chaque clone (clonotypique) se substituant au point de cassure de t(14;18).…”

“…6 Exome-seq : séquençage de l'exome à haut débit. [9]. De plus, une excellente correspondance existe entre le taux et la relevance/récurrence des altérations et les différents stades de progression vers le lymphome folliculaire (FLIS < lymphome folliculaire bas grade < lymphome folliculaire haut grade).…”