Genetic features of patients with PAX5^AMP. (A) Data for the 77 patients with intragenic amplification of PAX5 identified at diagnosis. The copy numbers for each PAX5 exon and the other genes targeted by the P335 IKZF1 MLPA kit are shown. Cytogenetic results were available for 57 patients, with abnormalities involving the short arm of chromosome 9, trisomy 5, and monosomy 7 being the most common recurrent chromosomal abnormalities. †In patient 31, the probe ratio values for exons 2 and 5 were just below the cutoff of 2 for ≥4 copies; because the percentage of blast cells was low at 83.5%, this result was interpreted as amplification. ‡In patient 69, MLPA showed that exon 2 had a ratio of 2.42 and exon 5 of 1.69; however on the single-nucleotide polymorphism array, exons 2 to 5 were amplified. (B) Data from 9 matched diagnosis-relapse pairs. *In patient 37, the difference in copy number of the amplified exons between diagnosis and relapse was due to reduced percentage of blasts at relapse. **P2RY8-CRLF2 fusion assessed by MLPA, FISH, and/or reverse-transcriptase polymerase chain reaction. ***Patient 16 presented with partial trisomy of chromosome 5 as a result of an unbalanced translocation involving chromosomes 1 and 5: 47,XY,der(1)(1qter-1p21::5q?34-5qter),+der(5)(5pter-5q15::1p21-1pter).