Abstract 323: Early detection of cytogenetic switch from monoallelic to biallelic 13q14 deletion using BCL-2 index in CLL
Authors: Heba A. Degheidy, Fatima Abbasi, Gerald E. Marti
Journal: Cancer Research (2010)

Abstract Monoallelic deletion of 13q14.3 is the most common cytogenetic abnormality in chronic lymphocytic leukemia (CLL). The recently described mir15a/16-1 mutation can result in increased BCL-2 expression reflecting 13q14 status. We present a case of CLL with a transient bimodal BCL-2 subclone. The patient is a 60 years old female, Rai stage IV, with a ten-year history of CLL. Prognostic markers included: mutated IgVH, Zap70, CD38 and CD49d negative, with 75 % monoallelic 13q14 deletion at the time of diagnosis. At year ten, seven-color flow cytometric evaluation was performed twice within a three month interval showed three subpopulations. BCL-2 mean fluorescence intensity (MFI), and BCL-2 index were estimated on each population. Based on forward scatter (FS) vs. side scatter (SS), and BCL-2 MFI, these cells were sorted. Interphase FISH was performed on sorted cells using D13S319 spectrum orange/LSI 13q34 spectrum green probe to define 13q14x1, 13q14x2, and diploid cells. A lymphoid population was identified by CD45 vs. SS gating. Using FS vs. SS 90.6% were small lymphoid cells (SL1) and 6.4 % were large lymphoid cell (LL1). The overall small lymphocyte population showed 1% diploid cell, 78% 13q14x1, 21% 13q14x2, with BCL-2 index 1.9. The CD19+CD5+ (SL1) population could be further sub-divided into two distinct malignant BCL-2 subclone. Each subclone had a different BCL-2 index, and different percentage of (13q14x1, 13q14x2). The first subclone (42.8%) brightly expressed BCL-2 (SL1B), and showed 59% 13x14x1, and 41% 13q14x2 with a BCL2 index of 3.1. The second subclone (57.2%) dimly expressed BCL-2 (SL1D), and showed 89% 13q14x1, 10.5 % 13q14x2, and 0.5 % diploid cell with a BCL2 index of 1.1. Both subclone were : kappa+, CD5+, CD19+,CD20+,CD27+,CD23+,CD45+, and they were negative for CD38, CD49d,and ZAP-70 . The 6.4 %(LL1) population showed 2% diploid cell, 59% 13q14x1, 39% 13q14x2, with BCL-2 index 3.5.A second sample three month later showed one uni-modal homogenous BCL-2 population within the small lymphoid cells (SL2), and a decreased in the percentage of large lymphoid cell population (LL2). Both SL2, and LL2 showed increased in the BCL-2 index compared to the first sample. SL2 (93.5 %) showed 0.5 % diploid cell, 61.5% 13q14x1, 38 % 13q14x2, with BCL-2 index 2.2, and LL2 (2.9 %) showed 1.5% diploid cell, 52.5% 13q14x1, 46% 13q14x2, and BCL-2 index 4.5. This case demonstrates that there may be a relationship between the levels of BCL-2 MFI in the CLL lymphocyte, and the relative proportions of leukemia cells having either 13q14x1, or 3q14x2. Our study is the first to explore the importance of identification of subclones within a patient harboring different BCL-2 MFI at any given time. This denotes a difference in 13q14 status, and might signal the start of a new phase of the disease. This type of analysis enabled us to time the occurrence of events if we have the BCL-2 index base line for the clone at the time of initial diagnosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 323.