Poster Board III-891
Causal overexpression of BCL2 protein in follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL) can be deregulated either by chromosome translocation t(14;18)(q32;q21) or by copy number increase (CNI) of the BCL2 gene, the latter of which includes gains of 18q and extra- or intra-chromosomal amplification. To study the utilization and advantages of interphase fluorescence in situ hybridization (FISH) testing, we retrospectively analyzed abnormal results from 226 consecutive cases with FL or DLBCL using a dual-color dual-fusion t(14;18)/IGH-BCL2 probe (Abbott, IL) performed on various types of specimens such as paraffin embedded tissue, lymph nodes and bone marrow aspirates. The t(14;18) was found in 133 cases (58.8%) with 5 of them also having one extra BCL2 signal, whereas the remaining 93 (41.2%) cases had increased copy number of BCL2 with a range of 3 to 60. In the CNI group, there were two patterns observed: scattered signals seen in the vast majority of cases; and large clusters of intrachromosomally amplified signals observed in two cases. In a concurrent metaphase cytogenetic analysis on the same tonsil sample in one patient with DLBCL, the amplified BCL2-containing segments were present as homogeneously staining region (hsr) on chromosome 13q as well as 18q with no double minutes or marker chromosomes detected. The second highly amplified case was incidentally found to have enlarged lymph nodes during vascular surgery and diagnosed as follicular lymphoma grade 1/3. Interestingly, FISH on paraffin embedded lymph nodes showed one large cluster of amplified BCL2 with an IGH signal within each cluster, suggesting a coexisting translocation t(14;18) and an amplification of BCL2 per se. The FISH patterns in these two highly amplified cases seem to represent a tandem duplication of the BCL2 gene. Although t(14;18) and BCL2 amplification are generally considered to be mutually exclusive in lymphomagenesis, our latter case may be the first reported one where t(14;18) and BCL2 amplification occurred concomitantly. Our study demonstrated that FISH testing with its high specificity, sensitivity and easy visibility for individual cells from various tissue types can simultaneously detect translocations and copy number alterations, provide valuable diagnostic/prognostic information in lymphoma stratification, and complement conventional cytogenetics and comparative genomic hybridization.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.