Abstract 839 Hematology-Oncology I Platform, Saturday, 5/1

Background: Hyperdiploidy with more than 50 chromosomes is the most common cytogenic abnormality in acute lymphoblastic leukemia (ALL) and is seen in 25-50% of children over the age of one year who suffer from this disease. Conventional cytogenetic analysis of banding patterns in hyperdiploid cells is often difficult due to the frequently fuzzy appearance and the compact nature of the metaphase spreads. We used spectral karyotyping (SKY) on metaphase spreads from 17 children with ALL and hyperdiploidy in order to detect numerical and structural rearrangements.

Methods: Spectral karyotyping combines charge-coupled device (CCD) imaging with Fourier spectroscopy. An interferometer is used to assess the spectrum of fluorescence wavelengths and a computer program allows the simultaneous visualization of all human chromosomes in different pseudocolors

Results: All numerical changes were fully characterized and a non-random pattern of chromosomal gain was identified. The most common gains included chromosomes X, 4, 6, 10, 14, 18 and 21. Thirteen structural rearrangements were also detected, of which 10 were previously unidentified using standard cytogenetic methods. Seven of these rearrangements had a documented prognostic impact, e.g. t(12;21), t(9;22) and t(8;14), whereas the other rearrangements have not been previously reported.

Conclusion: Spectral karyotyping is a powerful method to detect chromosomal changes. The method will lead to increased knowledge about the pattern of chromosomal gains and structural abnormalities. It will improve the possibility to evaluate the validity of specific numerical changes, as well as resolve marker chromosomes and detect new structural aberrations.