- 1 Northern Genetics Service, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne
- 2 Department of Haematology, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne
- 3 Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne
- 4 Department of Cellular Pathology, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK
- Correspondence: Chris Bacon, Northern Institute for Cancer Research, Paul O’Gorman Building, Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK. Tel.: +44 191 2464404; Fax.: +44 191 2464301; Email:
Fusion tyrosine kinases involving anaplastic lymphoma kinase (ALK) are central to the pathogenesis of numerous malignancies, in which they represent important diagnostic and therapeutic targets.1 Van Roosbroeck et al. recently reported in this Journal the elegant characterization of a cytogenetically cryptic SEC31A-ALK fusion arising from complex chromosomal rearrangements in a case of ALK-positive large B-cell lymphoma (LBCL).2 As this fusion had previously been identified only in a single case of inflammatory myofibroblastic tumor,3 the authors proceeded to show that it produced a constitutively active fusion tyrosine kinase able to transform hematopoietic cells in vitro and susceptible to an ALK-selective small molecule kinase inhibitor. However, whether the SEC31A-ALK fusion is a recurrent oncogenic event in lymphoma remained unknown. We now report a second case of ALK-positive LBCL harboring a complex SEC31A-ALK fusion, confirming it as an important lymphomagenic oncogene and further highlighting difficulties in its cytogenetic identification.
ALK-positive LBCL is a rare tumor of post-germinal center B cells which occurs most frequently in adult males, many of whom present with advanced disease and pursue an aggressive clinical course.4–5 Most cases carry a t(2;17)(p23;q23)/CLTC-ALK while a minority harbor a t(2;5)(p23;q35)/NPM-ALK.4–8 The patient reported here was clinically typical. He was a 66-year old man with a short history of weight loss, night sweats and dysphagia. Serial imaging showed rapid development of widespread lymphadenopathy, and numerous lymphomatous deposits in the liver and bones. An inguinal lymph node biopsy showed a typical diffuse and sinusoidal infiltrate of large, EBV-negative, immunoblastic/plasmablastic lymphoid cells (Figure 1A) which expressed CD138, IRF4, EMA, CD4, CD45 and perforin, but not several other B- or T-cell antigens, and showed lambda immunoglobulin light chain restriction. ALK was expressed with a granular cytoplasmic staining pattern (Figure 1B). Bone marrow and duodenal biopsies were similarly involved (Ann Arbor stage 4B). The patient was treated with multi-agent chemotherapy but died three weeks after diagnosis.
Cytogenetic analysis revealed the karyotype 45,XY,der(1;17)(q10;q10),t(2;4)(p2?4;q21) (Figure 1C). Although expression of ALK by the neoplastic cells suggested a translocation involving ALK at 2p23, the breakpoint on chromosome 2 appeared to be at 2p24–25, telomeric to ALK. Fluorescence in situ hybridization (FISH) using an ALK breakapart probe nevertheless showed a split signal pattern in which the 5′ (centromeric) and 3′ (telomeric) elements were clearly separated in both interphase and metaphase cells. However, both signals remained nearby in interphase cells and in metaphases they were seen to be in proximity, in the normal orientation, on the p arm of der(2) (Figure 1D-E). These results suggested a complex rearrangement on der(2) involving ALK and a gene at 4q21-qter. Prompted by the report of Van Roosbroeck et al.,2 we investigated the involvement of SEC31A on 4q21 in the formation of a SEC31A-ALK fusion. FISH using an in-house SEC31A breakapart probe showed a split signal in which the 5′ (telomeric) element hybridized to der(2) and the 3′ (centromeric) element remained on der(4) (Figure 1F). RT-PCR was subsequently performed on RNA isolated from fixed lymphoma tissue using SEC31A exon 24 and ALK exon 20 primers, designed to identify the previously reported SEC31A-ALK fusion.2–3 This yielded a correctly-sized PCR product which, when sequenced, confirmed the expected in frame SEC31A-ALK fusion transcript (Figure 1G). In all three SEC31A-ALK translocations now reported, complex rearrangements involving the two partner genes have been observed.2–3 These were probably required to generate a functional SEC31A-ALK fusion, as the relative transcriptional orientation of the two genes precludes its formation by a simple reciprocal translocation. The requirement for a complex rearrangement probably underlies the comparative rarity of SEC31A-ALK amongst ALK fusions. A simple scenario that may be postulated in the present case is t(2;4)(p2?4;q21) followed by inversion of a segment of der(2) including the 3′ ends of SEC31A and ALK, bringing together the 5′ end of SEC31A and the 3′ end of ALK. Unfortunately, whole chromosome painting to further characterize the der(2) gave equivocal results and we were unable to detect the reciprocal ALK-SEC31A transcript by RT-PCR.
This report complements that of Van Roosbroeck et al.,2 confirming SEC31A-ALK as a recurrent event in ALK-positive LBCL. Recognition of this translocation in clinical practice is important for diagnosis of these lymphomas, which are probably under-recognised by histopathology alone, as they often have an aggressive clinical course which may warrant a modified treatment approach and as they may be susceptible to newly developed ALK kinase inhibitors. Cytogeneticists should be aware of the spectrum of complex rearrangements which may underlie SEC31A-ALK fusions. In particular, since ALK breakapart probes may be only minimally separated, vigilance is necessary in the FISH analysis.
The authors would like to thank Lisa Grady (Northern Genetics Service) for DNA sequencing. CMB was supported by a Senior Clinician Scientist Fellowship from The Royal College of Pathologists, The Health Foundation and The Pathological Society of Great Britain and Ireland.
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