CRLF2 and acute lymphoblastic leukemia: It utilizes targeted DNA copy number profiling by multiplex-ligation dependent probe amplification (MLPA) assays to identify IKZF1 deletions co-occurring with deletions of either PAX5, CDKN2A, CDKN2B or the pseudoautosomal region 1 (PAR1) at Xp22.33/Yp11.31 (as a surrogate for P2RY8::CRLF2), which are enriched in high risk leukemia subtypes such as BCR::ABL1-like ALL; but excludes cases with deletion of ERG, which is common in favorable risk DUX4-rearranged (DUX4r) ALL (7, 8, 10, 18, 19).