The cytogenetic hallmark of well-differentiated liposarcoma (WDLS) is a giant marker chromosomes containing amplified genes from chromosome 12q13-q15. Here, we have employed SKY and high-resolution 244K oligonucleotide array CGH to characterize rearrangements and amplifications in a new WDLS cell line (GOT3) with a giant marker chromosome derived from chromosomes 12, 1, and X. The most prominent amplifications included 144 genes in 12q11-q21.2, 201 genes in 1q23.3-q44, and six genes in 13q32.1-q32.2. In the 12q amplicons, MDM2 showed the highest level of amplification followed by LYZ, HMGA2 (5'-part), TSPAN8, CNOT2, YEATS4, CDK4, GNS, HELB, and TSFM. Expression analysis of genes from the three major amplicons revealed that several highly amplified potential target genes, including HMGA2, MDM2, YEATS4, CDK4, PKP1, IPO9, and SOX21, were strongly overexpressed. Studies of cell cycle controlling proteins that interact with CDK4 and MDM2 revealed an abnormally strong expression of cyclins D1 and E. The selective high-level amplification of the 5'-part of HMGA2, including the DNA-binding domains, suggests that this gene is a major target of amplifications in WDLS. Our results also identify several novel candidate genes of potential pathogenetic and therapeutic importance for WDLS.