ERG-deletions occur recurrently in acute lymphoblastic leukemia, especially in the DUX4-rearranged subtype. The ERG-deletion was shown to positively impact prognosis of patients with IKZF1-deletion and its presence precludes assignment into IKZF1plus group, a novel high-risk category on AIEOP-BFM ALL trials. We analyzed the impact of different methods on ERG-deletion detection rate, evaluated ERG-deletion as a potential marker for DUX4-rearranged leukemia, studied its associations with molecular and clinical characteristics within this leukemia subtype, and analyzed its clonality. Using single-nucleotide-polymorphism array, genomic polymerase chain reaction (PCR) and amplicon-sequencing we found ERG-deletion in 34% (16 of 47), 66% (33 of 50) and 78% (39 of 50) of DUX4-rearranged leukemia, respectively. False negativity of ERG-deletion by single-nucleotide-polymorphism array caused IKZF1plus misclassification in 5 patients. No ERG-deletion was found outside the DUX4-rearranged cases. Within DUX4-rearranged leukemia, the ERG-deletion was associated with higher total number of copy-number aberrations, and, importantly, the ERG-deletion positivity by PCR was associated with better outcome [5-year event-free survival (EFS), ERG-deletion-positive 93% vs. ERG-deletion-negative 68%, P=0.022; 5-year overall survival (OS), ERG-deletion-positive 97% vs. ERG-deletion-negative 75%, P=0.029]. Ultra-deep amplicon-sequencing revealed distinct co-existing ERG-deletions in 22 of 24 patients. In conclusion, our data demonstrate inadequate sensitivity of single-nucleotide-polymorphism array for ERG-deletion detection, unacceptable for proper IKZF1plus classification. Even using more sensitive methods (PCR/amplicon-sequencing) for its detection, ERG-deletion is absent in 22-34% of DUX4-rearranged leukemia and does not represent an adequately sensitive marker of this leukemia subtype. Importantly, the ERG-deletion potentially stratifies the DUX4-rearranged leukemia into biologically/clinically distinct subsets. Frequent polyclonal pattern of ERG-deletions shows that late origin of this lesion is more common than has been previously described.

CLIP Childhood Leukaemia Investigation Prague Department of Paediatric Haematology and Oncology 2nd Faculty of Medicine Charles University Prague

CLIP Childhood Leukaemia Investigation Prague Department of Paediatric Haematology and Oncology 2nd Faculty of Medicine Charles University Prague University Hospital Motol Prague Czech Republic

Department of Paediatric Haematology and Oncology 2nd Faculty of Medicine Charles University Prague University Hospital Motol Prague Czech Republic

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