Detection of t(11;18)(q21;q21) by interphase fluorescence in situ hybridization using API2 and MLT specific probes

The translocation of chromosome 11, long arm, region 2, band 1, to chromoso me 18, long arm, region 2, band 1 (t(11;18)(q21;q21)) represents a recurren t chromosomal abnormality in extranodal marginal zone B-cell lymphoma (MZBC L) of mucosa-associated lymphoid tissue (MALT) type and leads to a fusion o f the apoptosis inhibitor-2 (API2) gene on chromosome 11 and the MALT lymph oma-associated translocation (MLT) gene on chromosome 18. A 2-color fluores cence in situ hybridization (FISH) assay, which can be used for the detecti on of t(11;18) in interphase nuclei and metaphase chromosomes on fresh and archival tumor tissue, was developed. The P1 artificial chromosome (PAC) cl one located immediately telomeric to the MLT gene and the PAC clone spannin g the API2 gene were differentially labeled and used to visualize the deriv ative chromosome II resulting from t(11;18), as evident by the overlapping or juxtaposed red and green fluorescent signals. The assay was applied to i nterphase nuclei of 20 cases with nonmalignant conditions and 122 B-cell no n-Hodgkin's lymphomas (NHLs), The latter group comprised 20 cases of nodal follicle center cell lymphoma and diffuse large B-cell NHL, 10 cases of gas tric diffuse large B-cell lymphoma, 10 cases of hairy cell leukemia, and 82 cases of MZBCL (41 extranodal from various locations, 19 nodal, and 22 spl enic MZBCL) including 35 cases with an abnormal karyotype, 2 of which revea led t(11;18). By interphase FISH, t(11;18) was detected in 8 gastrointestin al low-grade MALT-type lymphomas including the 2 cytogenetically t(11;18)() cases. In the 8 t(11;18)(+) cases, the FISH results were confirmed by rev erse transcriptase-polymerase chain reaction (RT-PCR) using API2 and MLT sp ecific primers. Our results indicate that t(11;18)(q21;q21) specifically ch aracterizes a subgroup of low grade MZBCL of the MALT-type and that the FIS H assay described here is a highly specific and rapid test for the detectio n of this translocation. (Blood, 2000;96:2215-2218) (C) 2000 by The America n Society of Hematology.