Hidden aberrations diagnosed by interphase fluorescence in situ hybridisation and spectral karyotyping in childhood acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) is the most common oncologic disease in childhood, accounting for approximately 25% of all paediatric malignancies. Based on clinical risk criteria and modern laboratory investigations including immunophenotyping, cytogenetics and molecular genetics, patients can be divided into prognostic groups and assigned to risk-adjusted treatment protocols. The karyotype is an independent prognostic indicator and has for some aberrations that are associated with a poor outcome a direct impact on the choice of treatment. Cytogenetic analysis in ALL is often hampered by poor chromosome morphology, few malignant metaphases, undetectable chromosomal rearrangements due to regions of a similar size and banding pattern and sometimes only normal metaphases derived from normal cells are found after cell culture. Structural as well as numerical aberrations may therefore remain undetected using conventional G-banding. The application of modern molecular cytogenetic techniques including a broad set of fluorescence in situ hybridisation (FISH) methods and recent developments in comparative genomic hybridisation to DNA microarrays, together with molecular methods such as Southern blotting and RT-PCR has greatly improved the detection rate of genetic changes in ALL. This review emphasises the value of increasing the resolving power of the cytogenetic investigation by spectral karyotyping (SKY) and interphase FISH in identifying prognostically important and novel chromosomal rearrangements as a complement to conventional banding analysis. The results of investigations performed on cases with ALL have shown that interphase FISH is valuable and in many cases even mandatory for the detection of prognostically important genetic abnormalities and should therefore consistently be employed in the routine cytogenetic investigations in ALL. Likewise, SKY is a valuable tool for the cytogenetic analysis. Thus, the results of several different investigations described in this review revealed that SKY yielded additional information in 97/157 (62%) cases with chromosomal aberrations detected by G-banding, and in 10/66 (15%) cases with normal G-banding.