The Majority of Immunohistochemically BCL2 Negative FL Grade I/II Carry A t(14;18) with Mutations in Exon 1 of the BCL2 Gene and Can Be Identified with the BCL2 E17 Antibody
Patrick Adam, Rosalie Baumann, Irina Bonzheim, Falko Fend, Leticia Quintanilla-Martinez. Eberhard-Karls-University, Tubingen, Baden-Wurttemberg, Germany
Background: Follicular lymphoma (FL) is characterized by the chromosomal translocation t(14;18)(q32;q21) resulting in constitutional overexpression of the antiapoptotic protein BCL2. However, in 10-15% of FL grade I/II immunohistochemical (IHC) staining for BCL2 remains negative. The aims of this study were 1) to investigate the incidence of IHC BCL2 negative FL grade I/II in our series, 2)To analyze the BCL2 IHC negative FL with the new BCL2 antibody (clone E17) 3) To perform FISH analysis for the t(14;18) and 4) to elucidate the molecular mechanism of BCL2 negativity.
Design: FL grade I/II diagnosed between 01/2005 and 08/2011 at the Institute of Pathology of the University of Tübingen, Germany were included in the study. All cases were stained with the standard BCL2 antibody (clone 100D5; DCS). All BCL2 negative cases were subsequently stained with the BCL2 antibody, clone E17 (Zytomed) and analyzed by FISH using a BCL2 break-apart probe (LSI BCL2 BAP, Vysis). Exon 1 of the BCL2 gene, where the epitope of the standard BCL2 antibody resides was amplified and sequenced.
Results: Of the 240 cases of FL grade I/II identified, 23 cases (9.6%) were negative with the standard BCL2 antibody. Of these, 13 cases (57%) were positive for the E17 antibody and 10 cases (43%) remained negative. FISH analysis demonstrated a BCL2 break, indicative of a t(14;18) in all E17 positive cases, whereas the E17 negative cases showed no BCL2 alterations. Two of the E17 negative cases carried a BCL6/IGH translocation. Mutation analysis of BCL2 exon 1 revealed point mutations resulting in amino acid substitutions in all 9 analyzable E17 positive cases with a hot spot around codon 144.
Conclusions: 1) The incidence of IHC negative FL grade I/II in our series is comparable to published data. 2) The E17 antibody identifies the majority of BCL2 „negative“ FL grade I/II and correlates with the presence of the t(14;18). 3) The negativity with the standard BCL2 antibody is due to point mutations in exon 1 of the BCL2 gene where the epitope of the antibody resides. 4)The molecular pathogenesis of the BCL2 (E17), t(14;18) negative FL grade I/II remains to be determined.
Monday, March 19, 2012 11:00 AM
Platform Session: Section C, Monday Morning