e15110 Background: The alteration of serum-iron level during chemotherapy is already reported (Follezou, NEOPLASMA 1985). However, the correlation to prognosis has not been evaluated. The aim of this study was to evaluate the correlation between prognosis and serum-iron level in advanced / metastatic colorectal cancer (aCRC / mCRC) patients treated by FOLFOX / FOLFIRI. Methods: Serum-iron levels, hemoglobin, AST and ALT serum levels in immediately pre and post chemotherapy were analyzed in 58 aCRC / mCRC patients received FOLFOX-4 / FOLFIRI therapy between April 2005 and September 2008. 26 patients received FOLFOX-4 / FOLFIRI therapy as the final chemotherapy died by the time of analysis. These patients were categorized into the high increase group and the low increase group using 200% increase as cut-off value and the prognosis was compared. Results: Mean serum-iron levels in immediately pre and post chemotherapy were 71.7±29.0μg/dl and 186.8±83.2μg/dl, respectively, and significant increase after chemotherapy was observed (p<0.001). This increase was transient and returns to pre chemotherapy level by the start of next course. This alteration was always observed on the chemotherapy. The median survival times from the initiation of FOLFOX-4 / FOLFIRI therapy for the high increase group (n: 5) and the low increase group (n: 21) were 487 and 182 days, respectively, and was significantly better in the high increase group (p=0.004). The alterations of hemoglobin, AST and ALT serum levels in immediately pre and post chemotherapy were not observed. Conclusions: It is suggested that serum-iron increase is a biological response not attributed to leakage from erythrocyte and hepatocyte. Significantly better prognosis in high serum-iron group may suggest the usefulness of serum-iron level to distinguish responder and non-responder in FOLFOX-4/FOLFIRI therapy. No significant financial relationships to disclose.