Objective: To study the genomic abnormality underlying the blast crisis of chronic myeloid leukemia(CML).

Methods: 15 CML patients in blast crisis (BC), 3 in accelerated phase (AP) and 20 in chronic phase (CP) were analyzed by conventional cytogentics, comparative genomic hybridization (CGH) and dual color chromosomal painting.

Results: Philadelphia (Ph) chromosome was identified in every case studied. Only 5 among 20 CP patients had additional abnormalities while 12 out of 14 patients with disease progression (BC + AP) showed extra numerical and/or structural chromosmal aberrations. Cytogenetically, the most common chromosome gains during BC and AP were double or triple Ph chromosome(5/14), trisomy 8(5/14), trisomy 7(1/14) and 17 (1/14). Three cases showed the same region being involved in translocations t(1;17)(q12-21;q10), t(1;10) (q12-21;q26) and t(1;11)(q12-21;p15). CGH analysis detected genetic imbalances in 8 cases. In one case, a very complex chromosmal translocation del(3), del(6)(q13-21), der(6)t(17;3;6), der(17)t(6;17) was characterized by chromosomal painting.

Conclusions: We find that the combined use of CGH, chromosomal painting, and classic cytogenetic analysis allows a better evaluation of the genomic aberration involved in CML blastic transformation, and offers new directions for its further molecular investigation.