CEA response and depth of response (DpR) to predict clinical outcomes in patients (pts) with metastatic colorectal cancer (mCRC) treated with first-line cetuximab plus oxaliplatin-based chemotherapy: A sub-analysis of the JACCRO CC-05/06 trials.

648Background: Carcinoembryonic antigen (CEA) decrease was faster and greater in cetuximab (cet) treatment than bevacizumab treatment and correlated with prolonged survival in mCRC pts receiving FOLFIRI plus cet (Michl M, et al. Ann Oncol 2016). We investigated if the CEA decrease is a surrogate for DpR reported to be associated with clinical outcomes. Methods: This study evaluated the association between the percentage of CEA decrease or DpR and clinical outcomes in pts with KRAS exon 2 wild-type from 2 phase II trials of 1st-line therapy; JACCRO CC-05 of cet plus FOLFOX (n= 57, UMIN000004197) and CC-06 of cet plus SOX (n= 61, UMIN000007022). The association was analyzed using Spearman’s rank correlation coefficient. The cut-off value of 75% CEA decrease was used for CEA response to discriminate CEA responders according to the previous report. The DpR was defined as the percentage of tumor shrinkage at the nadir as compared with the baseline values. Results: In total of 113 pts of the 2 trials in the ful...