Chromosome 18 breakpoint in t(11;18)(q21;q21) translocation associated with MALT lymphoma is proximal to BCL2 and distal to DCC.

The t(11;18)(q21;q21) translocation has recently been identified as a recurring chromosomal abnormality in a subset of extranodal marginal zone B-cell lymphoma, a low-grade lymphoma of mucosa-associated lymphoid tissue (MALT). Neither the 11q21 nor the 18q21 breakpoints have been characterized by molecular genetic analysis. As a prelude to isolation of the gene(s) involved in this translocation, we have mapped the 18q21 breakpoint region by fluorescence in situ hybridization (FISH) of YAC and PAC clones. We mapped 37 YACs assigned to a 29-cM region within the chromosomal band 18q21. Using nine of these YACs in single- and/or dual-color FISH to analyze three cases of MALT lymphomas with the t(11;18)(q21;q21) translocation, we localized the breakpoints within a 1.6-Mb nonchimeric YAC (938E1). This YAC is useful for the detection of the translocation in metaphase and in interphase cells. A nonchimeric YAC contig of an 8-cM region around the breakpoint comprising nine YACs and a PAC contig of YAC 938E1 were constructed, which enabled the refinement of the breakpoint region in the proximal region of the YAC within a <820-kb segment. This breakpoint is proximal to the BCL2 locus and distal to DCC and DPC4 loci in chromosomal band 18q21.