The ACHIEVE-2 trial, as part of the IDEA Collaboration, was a multicenter trial to randomize patients with high-risk stage II colon cancer to either 3 versus 6 months of adjuvant FOLFOX/CAPOX. The eligibility criteria in the trial included postoperative serum CEA value of <10 ng/ml at registration. Results: Of 514 patients analyzed, median CEA value was 1.9 (range, 0.5e9.9). 48 (9%) patients had a CEA of !5.0 ng/ml and 466 (91%) had a value of <5.0. 3-year DFS was 86% in the !5.0 group and 88% in the <5.0 group, with a hazard ratio (HR; reference, <5.0) of 1.27 (95%CI, 0.58e2.79). Multivariate analysis showed that CEA was not an independent prognostic factor (P¼0.5117). However, in the subgroup of patients with T3N0 tumor (n¼330), 3-year DFS in the !5.0 group was significantly lower than that in the <5.0 group (84% vs 95%) with a HR of 2.83 (1.04e7.75), whereas in patients with T4N0 tumor (n¼184), this relationship was opposite; 3-year DFSs in the !5.0 and <5.0 groups were 88% and 77%, respectively, with a HR of 0.51 (0.12e2.12). The interaction test for T-factor (T3 vs T4) by CEA (!5.0 vs <5.0) was significant (P¼0.0479).Conclusions: Postoperative CEA was prognostic in patients with T3N0 tumor, whereas this association did not hold in T4N0 tumor, suggesting that the characteristics of T4N0 tumor might have diluted the prognostic effect of CEA. Further analyses incorporating T4N0 tumor's features, such as microsatellite status, would be warranted.Clinical trial identification: UMIN000013036.
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