BCR/ABL rearrangement with b3a3 fusion transcript in a case of childhood acute lymphoblastic leukemia

The role of BCR/ABL isoforms and their relationship to leukemia phenotype have been of major concern. Atypical BCR/ABL mRNA transcripts lacking exon a2 have been reported in 12 cases of acute lymphoblastic leukemia (ALL) to date; among them, a b3a3 type transcript has been reported only once in the childhood ALL. Reported here is the case of a patient with Philadelphia-positive (Ph⁺) ALL expressing a b3a3 type transcript, a rare type of BCR/ABL mRNA lacking ABL exon a2 sequences. Bone marrow showed a hypercellular marrow with leukemic blasts positive for CD10, CD19, CD79a, and cytoplasmic μ, which is consistent with pre-B ALL. The G-banding and fluorescence in situ hybridization analyses indicated Ph⁺. After the patient was diagnosed with ALL-L2, induction chemotherapy was performed and imatinib mesylate was thereafter given as the maintenance therapy. Sequencing analysis showed deletion of ABL a2 in the polymerase chain reaction product, which corresponded to a b3a3 fusion transcript. To our knowledge, this is the second report of an aberrant BCR/ABL product lacking ABL exon a2 in childhood ALL.