The third patient was a 14-year-old boy who was admitted to hospital due to a fever that had lasted for 5 days, and pain of the lower limbs. Lymphadenopathy, hepatosplenomegaly, and the infiltration of the central nervous system were not observed, but the WBC count was 3,900/microL, platelet count was 359,000/microL, and hemoglobin level was 9.5 g/dL. Bone marrow evaluation showed 69% blasts. The boy was diagnosed with B-cell precursor common positive ALL and chemotherapy was started in July 2019, according to the AIEOP-BFM ALL 2017 protocol. He was classified into the early non-high-risk group. According to the protocol cytogenetic analysis and FISH were performed on a bone marrow sample. G-banded chromosome analysis revealed a male karyotype 45,XY,-21,+mar/46,XY. The FISH study revealed no rearrangements in BCR/ABL1, KMT2A, or ETV6/RUNX1, but revealed 8-10 signals of RUNX1 in 24.4% of interphase cells (Fig. 3A). CytoScan HD array revealed amplification of arr[GRCh37] 21q22.11q22.3(31846769_47960084)x4. The size of amplification was 16.1 Mb and included following genes: OLIG2, TIAM1, ERG, ETS2, TMPRSS3, TFF2, TFF3, TFF1, DYRK1A, U2AF1, RUNX1, TMPRSS2, CSTB, and PTTG1IP. Furthermore, analysis showed duplication of the entire long arm of chromosome 9 and deletion within chromosome 14q23.2-q31.3 (Fig. 3B).