Morphologic, immunophenotypic and cytogenetic features of precursor B-ALL with CLN. (A) CLN (arrows) in variably sized blasts in BM smears from cases 1 and 2 (Wright-Giemsa stain, original magnification ×1000). (B) Representative immunophenotype of CLN⁺ B-ALL cases: CD34⁺CD19⁺CD20⁻CD10⁻ or CD10 dimly and partially positive. Dot plots of 4-color FCM analysis performed using a BD FACSCanto and analyzed with BD FACSDiva software. (C) Image of Affymetrix CytoScan HD whole-genome microarray showing 7p12.2 deletion as the sole clonal aberration (red arrow). (D) Zoomed in image of the 7p12.2 deletion showing loss of the entire IKZF1 gene. (E) FISH image showing a single green signal for IKZF1 in the first 2 cells (from left to right), which indicates 1 copy loss of IKZF1. The 2 red BRAF (7q34) signals serve as an internal chromosome 7 control. Comparison of CLN⁺, low-CLN⁺, and CLN⁻ frequencies with IKZF1 deletion (F), favorable cytogenetic abnormalities (ETV6/RUNX1 or high hyperdiploidy) (G), nonrecurrent cytogenetic abnormalities (H), normal karyotype (I), CD10 negativity or partial negativity (J), and day-29 BM MRD ≥ 0.01% (K).