The PAX5 is essential in normal B-cell lymphopoiesis and deregulation of PAX5 function is believed to contribute to leukemogenesis in B-ALL. We performed a comprehensive study using FISH, G-banding and IHC to identify PAX5 deletion and expression in 102 CD19+ clinical B-ALL cases (79 children and 33 adults) and investigated its relationship with common cytogenetic changes including BCR-ABL1, ETV6-RUNX1 and MLL rearrangements, and CDKN2A deletion. The incidences of translocations and deletions were 2.5% and 10.0% in children, and 0.0% and 18.2% in adults, respectively. The incidence of PAX5 deletion was higher than those of BCR-ABL1 (8.9%) or MLL rearrangements (5.1%) in children and than that of MLL rearrangement (3.1%) in adults. Most patients with PAX5 deletion (83.3% of children and 100.0% of adults with PAX5 deletion) had concurrent CDKN2A deletion. PAX5 deletions were detected both in patients with positive and negative PAX5 expression. In this study, we found that PAX5 is a common target in leukemogenesis of B-ALL along with CDKN2A. Owing to its frequent deletion in B-ALL, PAX5 could be used as one of the molecular markers in diagnosis and monitoring of the disease. No correlation between expression of PAX5 and deletion of PAX5 suggests allele-specific regulation.
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