BCR and mixed phenotype acute leukemia: MPAL with BCR::ABL1 fusion accounts for < 0.5% of all cases of acute leukaemia and 15% to 20% of all cases of MPAL, making BCR::ABL1 fusion the most common cytogenetic abnormality in MPAL.[1] Most transcripts have resulted from chromosomal breakpoints in breakpoint cluster region (BCR) introns 1, 13, or 14 and ABL1 intron 1 (known as e1a2, e13a2, or e14a2, respectively).