High frequency of t(14;18)-translocation breakpoints outside of major breakpoint and minor cluster regions in follicular lymphomas: improved polymerase chain reaction protocols for their detection.

The detection of t(14;18) translocations is widely used for the diagnosis and monitoring of follicular lymphomas displaying a high prevalence for this aberration. Cytogenetics, Southern blotting, and polymerase chain reaction (PCR) are commonly used techniques. It is generally believed that the vast majority of the breakpoints occurs on chromosome 18 in the major breakpoint region (mbr) and the minor cluster region (mcr). Yet, by improving long-distance PCR protocols we identified half of the breakpoints outside of these clusters. Our study included biopsies from 59 patients with follicular lymphoma. Seventy-one percent carried translocations detectable with our long-distance PCR protocol. The novel primer sets were derived from the hitherto uncharacterized 25-kb-long stretch between mbr and mcr that we have sequenced for this purpose. Sequence analysis of the novel breakpoints reveals a wide distribution between mbr and mcr displaying some clustering 16 kb downstream from the BCL2 gene. By including a primer for this intermediate cluster region in standard PCRs we could also improve the detection of t(14;18) translocations in formalin-fixed and paraffin-embedded biopsies. Our new PCRs are highly sensitive, easy to perform, and thus well suited for routine analysis of t(14;18) translocations for the primary diagnosis of follicular lymphoma and surveillance of minimal residual disease.