In T-cell acute lymphoblastic leukaemia (T-ALL) lacking TAL1d abnormality or TAL1 chromosomal rearrangements, heterozygous indel mutations in the region 7.5 kb upstream of TAL1 TSS result in de novo MYB binding motif (or even two motifs as in Jurkat cells) and thereby the emergence of TAL1-SE. Here, TAL1 is linked to T-cell acute lymphoblastic leukemia.