PAX5 fusion genes in t(7;9)(q11.2;p13) leukemia: a case report and review of the literature

BACKGROUND: B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is characterized by recurrent genetic alterations including chromosomal translocations. The transcription factor PAX5, which is pivotal for B-cell commitment and maintenance, is affected by rearrangements, which lead to the expression of in-frame fusion genes in about 2.5% of the cases. RESULTS: Using conventional cytogenetics, fluorescence in situ hybridization (FISH), and molecular methods, an additional case with a der(9)t(7;9)(q11.23;p13) resulting in the expression of a PAX5-ELN fusion gene was identified. Furthermore, a general review of leukemia harboring a t(7;9)(q11.2;p13) or der(9)t(7;9)(q11.2;p13), which occurs more often in children than in adults and shows a remarkably high male preponderance, is given. These cytogenetically highly similar translocations lead to the expression of one of three different in frame PAX5-fusions, namely with AUTS2 (7q11.22), ELN (7q11.23), or POM121 (7q11.23), which constitute the only currently known cluster of PAX5 partner genes. CONCLUSION: Our report underlines the recurrent involvement of PAX5 in different fusion genes resulting either from t(7;9)(q11.2;p13) or der(9)t(7;9)(q11.2;p13), which cannot be distinguished cytogenetically and whose discrimination requires molecular analysis.