Cryptic BCR-ABL fusion gene as variant rearrangement in chronic myeloid leukemia: molecular cytogenetic characterization and influence on TKIs therapy.

At diagnosis, about 5% of Chronic Myeloid Leukemia (CML) patients lacks Philadelphia chromosome (Ph), despite the presence of the BCR/ABL rearrangement. Two mechanisms have been proposed about the occurrence of this rearrangement: the first one is a cryptic insertion between chromosomes 9 and 22; the second one involves two sequential translocations: a classic t(9;22) followed by a reverse translocation, which reconstitutes the normal morphology of the partner chromosomes. Out of 398 newly diagnosed CML patients, we selected 12 Ph-negative cases. Six Ph-negative patients treated with tyrosine kinase inhibitors (TKIs) were characterized, in order to study the mechanisms leading to the rearrangement and the eventual correlation with prognosis in treatment with TKIs. FISH analysis revealed cryptic insertion in 5 patients and classic translocation in the last one. In more detail, we observed 4 different patterns of rearrangement, suggesting high genetic heterogeneity of these patients. In our cases, the BCR/ABL rearrangement mapped more frequently on 9q34 region than on 22q11 region, in contrast to previous reports. Four patients, with low Sokal risk, achieved Complete Cytogenetic Response and/or Major Molecular Response after TKIs therapy. Therapy resistance was observed in one patient with duplication of BCR/ABL rearrangement and in another one with high risk. Even if the number patient is inevitably low, we can confirm that the rare Ph-negative CML patients do not constitute a "warning" category, meanwhile the presence of further cytogenetic abnormalities remains an adverse prognostic factor even in TKI era.

Complex chromosomal rearrangements leading to MECOM overexpression are recurrent in myeloid malignancies with various 3q abnormalities.

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.

Additional chromosomal abnormalities in Philadelphia-positive clone: adverse prognostic influence on frontline imatinib therapy: a GIMEMA Working Party on CML analysis.

Additional chromosomal abnormalities (ACAs) in Philadelphia-positive cells have been reported in ∼ 5% of patients with newly diagnosed chronic myeloid leukemia (CML) in chronic phase (CP). Few studies addressing the prognostic significance of baseline ACAs in patients treated with imatinib have been published previously. The European LeukemiaNet recommendations suggest that the presence of ACAs at diagnosis is a "warning" for patients in early CP, but there is not much information about their outcome after therapy with tyrosine kinase inhibitors. To investigate the role of ACAs in early CP CML patients treated with imatinib mesylate, we performed an analysis in a large series of 559 patients enrolled in 3 prospective trials of the Gruppo Italiano Malattie Ematologiche dell'Adulto Working Party on CML: 378 patients were evaluable and ACAs occurred in 21 patients (5.6%). The overall cytogenetic and molecular response rates were significantly lower and the time to response was significantly longer in patients with ACAs. The long-term outcome of patients with ACAs was inferior, but the differences were not significant. The prognostic significance of each specific cytogenetic abnormality was not assessable. Therefore, we confirm that ACAs constitute an adverse prognostic factor in CML patients treated with imatinib as frontline therapy.