In this study, we used spectral karyotyping (SKY) and fluorescence in situ 
hybridization (FISH) as complementary techniques for the analysis of two 
therapy-related secondary myelodysplastic syndrome (t-MDS) cases with complex 
karyotypes, previously analyzed by G-banding. Different types of SKY's 
cytogenetic contributions include confirmation of G-banding results, 
identification of partially characterized rearrangements, identification of 
marker chromosomes unidentified by G-banding, and detection of cryptic 
reciprocal translocations. In particular, the ability of SKY to clarify a number 
of markers led to the comprehension of clonal evolution. The common aberration 
found in these two t-MDS cases was the fragility of chromosome 5 and monosomy of 
chromosome 18. We clearly present that the use of SKY combined with conventional 
G-banding analysis and FISH has assisted in the identification of important 
chromosomal events that may play a key role in the development of t-MDS.