Supplementary Material for: The recurrent atypical e8a2 BCR::ABL1 transcript with insertion of an inverted 55 base pair ABL1 intron 1b sequence: a detailed molecular analysis

Atypical BCR::ABL1 transcripts are found in approximately 2% of cases of chronic myeloid leukemia. It is important to detect them, since affected patients benefit from tyrosine kinase inhibitor therapy, similar to patients with typical BCR::ABL1 variants. In the rare e8a2 atypical BCR::ABL1 transcript two out-of-frame exons are fused, thus, interposed nucleotides are usually found at the fusion site to restore the reading frame. In approximately half of previously reported e8a2 BCR::ABL1 cases an inserted 55 bp sequence homologous to an inverted sequence from ABL1 intron 1b was detected. The generation of this recurrent transcript variant is not obvious. This work describes the molecular analysis of such an e8a2 BCR::ABL1 translocation from a CML patient. The genomic chromosomal breakpoint is identified, and the formation of this transcript variant is theoretically explained. The clinical course of the patient is reported, and recommendations are provided for the molecular analysis of future e8a2 BCR::ABL1 cases.