Three novel cytogenetically cryptic EVI1 rearrangements associated with increased EVI1 expression and poor prognosis identified in 27 acute myeloid leukemia cases

Abstract

In acute myeloid leukemia (AML), increased ecotropic virus integration site 1 protein homolog (EVI1) gene expression is prognostically unfavorable. Subsets of cases show 3q26 rearrangements, such as inv(3)(q21q26)/t(3;3)(q21;q26), frequently accompanied by chromosome 7 abnormalities. We investigated whether cytogenetically cryptic EVI1 rearrangements may cause EVI1 overexpression in myeloid malignancies without 3q26 abnormalities and investigated 983 patients with AML (n = 606) or myelodysplastic syndromes (MDS; n = 377) with normal karyotype (CN-AML/CN-MDS, n = 594) or chromosome 7 abnormalities (n = 389) for EVI1 rearrangements using interphase FISH. We identified cytogenetically cryptic EVI1 rearrangements in 27 patients (19 AML, 8 MDS): inv(3)(p24q26) [n = 10]; t(3;21)(q26;q11) [n = 9]; and der(7)t(3;7)(q26;q21) [n = 8]. Elevated EVI1 expression was detected in nearly all cases with cryptic EVI1 rearrangements: Median %EVI1/ABL1 was 92.8 (range: 29.8-146.1) in inv(3)(p24q26), 104.9 (41.4-176.3) in t(3;21)(q26;q11), and 101.8 (4.4-210.4) in der(7)t(3;7)(q26;q21). This was similar to median %EVI1/ABL1 of 73.9 (range: 7.3-585.6) in an independent cohort of inv(3)(q21q26)/t(3;3)(q21;q26) and 67.1 (2.3-410.7) in other 3q26/EVI1 rearrangements. Healthy controls showed median EVI1 expression of 0.5 (range: 0.0-5.8). Using SNP microarray and sequencing analyses, the breakpoints of der(7)t(3;7)(q26;q21) were assigned to CDK6 and centromeric of EVI1, and of t(3;21)(q26;q11) to be within EVI1 and NRIP1. Median overall survival in patients with cryptic EVI1 rearrangements was short, comparable to patients with inv(3)(q21q26)/t(3;3)(q21;q26) or other EVI1 rearrangements. Cryptic EVI1 rearrangements contribute to explain the clinical heterogeneity of CN-AML and are associated with elevated EVI1 expression and an unfavorable prognosis. Screening for cryptic EVI1 rearrangements by FISH may be particularly appropriate in CN-AML with elevated EVI1 expression or in AML/MDS patients with chromosome 7 abnormalities.