15567 Background: GCTs are the most common malignancy in young Caucasian males aged 20–40. With CDDP-based chemotherapy, highly effective treatment has been developed for the majority of patients with GCT. However, the molecular mechanisms underlying treatment response remain elusive. Therefore, we used a global proteomics approach to screen for changes induced in GCT cell lines by CDDP. Material and Methods: Global protein expression analysis of three GCT cell lines, NTERA2, 2102EP, and NCCIT, both untreated and treated with CDDP for 48 hours at the IC50, was performed using 2-dimensional gel electrophoresis. Differentially expressed proteins were analyzed using matrix-assisted laser desorption/ionization - time of flight (MALDI TOF) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Identification of proteins was performed using peptide mass-fingerprinting and NCBI/SwissProt and The Global Proteome Machine database search. Results: In total, 66 proteins were found to be differentially expressed comparing untreated and treated cells. Numbers of proteins showing upregulation under CDDP were 18 in NTERA2, 10 in NCCIT, and 9 in 2102EP, whereas 17 proteins were downregulated in NTERA2, 5 in NCCIT, and 7 in 2102EP. Identification of corresponding proteins was successful in 44 out of 66 spots (67%). Differential expression of 5 proteins was found in more than one cell line. One protein (Enolase 1) was consistently up-regulated in all three cell lines under CDDP. The identified proteins can be grouped into different categories: 15 are involved in DNA-binding/transcription, 8 in metabolism, 8 in protein folding/binding/chaperone, 6 in cell signaling/differentiation, 4 in apoptosis, and 3 in cytoskeleton/cell movement. Conclusion: The results of this screening approach identify factors differentially regulated during response to CDDP in GCTs, and reveal a specific response pattern for each cell line. This knowledge can help to identify therapeutic targets and factors potentially involved in treatment sensitivity and resistance. No significant financial relationships to disclose.