Chromosomal rearrangements involving 3q26 are recurrent findings in myeloid 
malignancies leading to MECOM overexpression, which has been associated with a 
very poor prognosis. Other 3q abnormalities have been reported and cryptic MECOM 
rearrangements have been identified in some cases. By fluorescence in situ 
hybridization (FISH) analysis, we investigated 97 acute myeloid 
leukemia/myelodysplastic syndrome patients with various 3q abnormalities to 
determine the role and the frequency of the involvement of MECOM. We identified 
MECOM rearrangements in 51 patients, most of them showed 3q26 involvement by 
chromosome banding analysis (CBA): inv(3)/t(3;3) (n = 26) and other balanced 
3q26 translocations (t(3q26)) (n = 15); the remaining cases (n = 10) showed 
various 3q abnormalities: five with balanced translocations involving 3q21 or 
3q25; two with homogenously staining region (hsr) on 3q; and three with other 
various 3q abnormalities. Complex rearrangements with multiple breakpoints on 
3q, masking 3q26 involvement, were identified in cases with 3q21/3q25 
translocations. Furthermore, multiple breaks were observed in two cases with 
t(3q26), suggesting that complex rearrangement may also occur in apparently 
simple t(3q26). Intrachromosomal gene amplification was another mechanism 
leading to MECOM overexpression in two cases with hsr on 3q. In the last three 
cases, FISH analysis revealed 3q26 involvement that was missed by CBA because of 
metaphases' suboptimal quality. All cases with MECOM rearrangements showed 
overexpression by real-time quantitative PCR. Finally, MECOM rearrangements can 
occur in patients with 3q abnormalities even in the absence of specific 3q26 
involvement, underlining that their frequency is underestimated. As MECOM 
rearrangement has been associated with very poor prognosis, its screening should 
be performed in patients with any 3q abnormalities.