•The case demonstrated a rare event of clonal heterogeneity by IKZF1 gene status in BCRABL1- ALL.•IKZF1 deletions are secondary events in ALL caused by clonal evolution during the treatment.•It's prognostic significance could be more crucial in BCR-ABL- rather than in BCR-ABL + ALL.•IKZF1 gene alterations may be determined and proved at the genome, expression and protein level.•IKZF1 deletions are suitable for MRD detection but not stable compared to Ig/TCR rearrangement.