Detection of t(14;18) by PCR of IgH/BCL2 fusion gene in follicular lymphoma from archived cytological smears

Abstract

According to WHO classification follicular lymphoma (FL) is a neoplasm composed of follicle centre (germinal centre) B-cells, which usually has at least a partially follicular pattern. Bone marrow (BM) infiltration by lymphoma occurs in 40-70% of cases at the time of diagnosis. The characteristic chromosomal translocation of follicular lymphoma is t(14;18)(q32;q21) with transposition of BCL2 oncogene to the regulatory region of immunoglobulin heavy chain gene IgH. Aim of this study was to determine the frequency of PCR detection of IgH/BCL2 in DNA samples isolated from archival cytological slides of lymph node aspirates, bone marrow and/or peripheral blood (PB) obtained from patients with histologically confirmed follicular lymphoma using primers and protocol proposed by BIOMED-2 consortium. We also compared molecular with cytomorphological findings in bone marrow/peripheral blood and tested this method of detection of IgH/BCL2 molecular marker in monitoring minimal residual disease (MRD) in routine clinical setting. DNA was successfully isolated from all archival cytological slides obtained by fine needle aspiration of lymph nodes as well as from 75% of smears of bone marrow aspirates from 19 patients. Fusion oncogene was detected in 10 of 19 patients (52%). For patients with PCR IgH/BCL2 positive lymph nodes, molecular test found BM infiltration in 5 cases (83%), while cytomorphology detected infiltration in three of eight cases (37%) available for comparison. May-Grünwald-Giemsa stained cytological smears can be used for PCR-based ancillary methods and the rate of detection of IgH/BCL2 rearrangement is similar to results reported for paraffin-embedded tissues. For patients with detectable baseline molecular marker, PCR is a highly suitable method for detection of bone marrow involvement and monitoring MRD.