A novel TRB@/NOTCH1 fusion gene in T-cell lymphoblastic lymphoma with t(7;9)(q34;q34).

BACKGROUND: In T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LBL), activating mutations of NOTCH1 are observed in more than 50% of cases, whereas the t(7;9)(q34;q34) involving NOTCH1 at 9q34 and TRB@ at 7q34 is an extremely rare but recurrent translocation.

PATIENT: A 41-year-old male with a large mediastinal mass, pleural effusion, and lymphadenopathy was diagnosed as having T-LBL. Lymphoma cells were positive for CD4, CD8, CD2, CD3, CD5, CD7, CD10, and TdT.

RESULTS: G-banding and spectral karyotyping of pleural effusion cells showed 47,XY,dup(1)(q21q32),t(7;9)(q34;q34),+20. Genomic polymerase chain reaction (PCR) revealed that the 5' end of TRB@ J1-5 was connected with the middle of NOTCH1 exon 25 (434 bp downstream from its 5' end) in a 'head-to-head' configuration on the der(9)t(7;9), although nine extra bases were inserted between the two genes. Reverse transcription-PCR confirmed expression of the TRB@/NOTCH1 fusion transcripts. Similarly, the 5' end of J1-5 was fused to the shortened exon 25 with nine extra bases. The NOTCH1 breakpoint in exon 25 was very close to transcription start sites of deleted Notch1 in murine T-ALL.

CONCLUSIONS: The TRB@/NOTCH1 fusion gene with a NOTCH1 breakpoint in exon 25, which has not previously been detected in four other reported cases with t(7;9), could lead to aberrant expression of the truncated NOTCH1 by TRB@ enhancer elements. The resultant NOTCH1 receptor deleting most of the extracellular domain may be implicated in the pathogenesis of T-LBL by ligand-independent, constitutive activation of the NOTCH1 pathway, suggesting avenues for future therapy with γ-secretase inhibitors.