Biological characterization of stage I follicular lymphoma according to extranodal or nodal primary origin and t(14;18) status using high‐resolution array‐based comparative genomic hybridization

Abstract

Biological characterization of stage I follicular lymphoma according to extranodal or nodal primary origin and t(14;18) status using high-resolution array-based comparative genomic hybridization To the Editor: Follicular lymphoma (FL) is the most frequent indolent lymphoma and has a variable clinical course. Although generally characterized by an indolent clinical behavior, many cases eventually transform to an aggressive large B-cell lymphoma [1]. Although most of the patients have advanced disease at presentation, approximately 10-20% of patients with FL present in limited stages (Stage I-II) [1]. In a retrospective analysis, more than half of patients with early stage FL remained untreated at a median of 6 or more years, and survival was comparable to that observed in patients undergoing immediate treatment [1]. FLs are generally characterized by the presence of the t(14;18)(q32;q21), which causes a fusion of the BCL2 oncogene with the immunoglobulin heavy chain joining region. The IGH/BCL2 rearrangement is a relatively specific molecular marker of FL, frequently used for diagnosis and monitoring of disease [2]. We have recently shown that the incidence of t(14;18) is significantly lower in limited stage FL and the status of t(14;18) appears to be predictive of clinical outcome [2]. Little is known of the molecular genetics of t(14;18)-negative FL or of the genetic differences between nodal and extranodal FL. Tagawa et al. has shown that trisomy 3 is a specific genomic aberration of t(14;18)-negative FL [3]. Leich et al. did not confirm this finding in their comparison of FLs with and without t(14;18) [4]. Katzenberger found that a distinctive subset of t(14;18)-negative nodal FL is characterized by a predominantly diffuse growth pattern and deletions in the chromosomal region 1p36 [5]. The goal of the current study was to characterize stage I FL using high resolution array-based comparative genomic hybridization (aCGH). Validation of findings in aCGH were performed on 20 stage I FL as well as an additional 28 stage I and II FL cases by both RNA gene expression and DNA copy number.Twenty stage I FL were identified from the pathology database of Stanford University as previously described [2]. Agilent 60-mer oligonucleotide microarrays were used to analyze DNA copy number variations. FFPE tissue DNA isolation, labeling, and microarray processing and feature extraction were preformed according to the manufacture instructions (Agilent Techologies, Santa Clara, CA). The obtained data was analyzed using both Agilent DNA Analytics 4.0 Software and CGH-miner (Stanford, CA) software. Only gains and losses identified by both methods were considered significant. Cases were compared both by origin from extranodal versus nodal site and by t(14;18) status. Genomic DNA was isolated using Ambion-Applied Biosystems (Foster City, CA) total nucleic Acid Isolation Kit. Multiplex PCR were performed on an ABI 7900HT PCR systems. RNA were isolated according to Ambion-Applied Biosystems. GAPDH was used as the reference gene. PCR we...