10534 Background: Metastatic colorectal cancer (mCRC) relies on the detachment of aggressive malignant cells from the primary tumor into the bloodstream, being this Circulating Tumor Cells (CTC) the principal source of the further metastasis. Clinically, the presence of CTC is associated with poor prognosis and there exists a clear necessity for more specific and efficient chemotherapies in the treatment of mCRC. Our aim was to overcome this adverse scenario through the massive molecular profiling of the CTC population isolated from mCRC patients. Methods: CTC’s were magnetically isolated by using anti-EpCAM coupled magnetic beads from 6 mCRC patients and 3 healthy controls. The presence of CTCs was evaluated by citokeratins 8, 18 and 19 staining. RNA from CTCs was amplified by a whole transcriptome amplification system (WTA) and resulting material was hybridized onto gene expression arrays. Bioinformatics were used to array analysis. Selected genes were validated by RT-qPCR. Results: 410 transcripts were found to specifically characterise the CTC population after array signals comparison between mCRC patients and controls. Gene-gene interaction analysis generated networks related with cell migration, adhesion or apoptosis resistance. Gene ontology revealed similar functions. Signalling pathways such as RhoA, PKA, ILK, integrins or actin cytoskeleton signalling were found as relevant in CTCs. Eleven genes (TGFB1, APP, TIMP1, CD9, CLU, ITGB5, LIMS1, RSU1, VCL, BMP6 and TLN1) were validated by real-time PCR in 20 mCRC patient and 10 control samples. All genes showed a significantly higher expression in patients (p<0.0001). Except from TLN1 and CD9, all genes had a prognostic value in terms of progression free survival (p<0.05). Conclusions: We described the molecular profiling of CTCs in stage IV CRC patients, characterized by a migratory and invasive phenotype. Specific and sensitive diagnostic/prognostic markers were obtained. Our strategy represents an innovative and promising approach in the clinical management of mCRC patients.