ASCO and ESMO guidelines have identified inadequate sampling of lymph nodes, pT4 primary tumors, obstruction or perforation, lymphovascular and perineural invasion, and poorly differentiated tumors as negative prognostic factors supporting the clinicians in treating their patients with stage II colon cancer (CC). However, the influence of histological subtypes on the risk of death or disease recurrence remains controversial.
The phase III, multicenter, randomized TOSCA trial compared 3 vs. 6 months of fluoropyrimidine-oxaliplatin adjuvant chemotherapy in 3,759 patients with high-risk stage II or stage III CC. Objective of this sub-study was to investigate the role of the histological subtype [(mucinous adenocarcinoma (MUC) or non-mucinous adenocarcinoma (NMUC)] on the impact of the treatment duration in terms of relapse-free survival (RFS) and overall survival (OS) in the subgroup of patients with high-risk stage II, grade 3 CC.
Out of 3,614 patients from 130 centres enrolled in the per-protocol population defined in the TOSCA trial, 85 MUC and 389 NMUC patients were included in this analysis. No statistical differences were found between 3 vs. 6 months groups in both histological subgroups in terms of baseline characteristics, except for tumor side. The proportion of patients with right-sided cancer was higher for patients with MUC than NMUC. A significant interaction between treatment duration and histology was observed on both RFS (p = 0.027) and OS (p = 0.017). In the subgroup of patients with MUC, worse RFS (adjusted hazard ratio [HR], 3.95; 95% confidence interval [CI], 1.03–15.17; p = 0.045) and OS (HR, 9.56; 95% CI, 1.14–79.98; p = 0.037) were detected for patients treated in the 3 months arm. No statistically significant differences were detected in the subgroup of patients with NMUC.
Both MUC and poorly differentiated subtypes have unfavorable clinical characteristics. Patients with MUC, grade 3, stage II CC require special attention and may need 6 months of oxaliplatin-based chemotherapy. Larger studies are required to clarify the possible negative effect of the histological subtype to improve the prognosis of these patients.
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