Introduction: Local advanced colon cancer is a high risk condition to develop tumor recurrences with poor survival. The current treatment is surgery and adjuvant chemotherapy based on fluoropyrimidines and oxaliplatin. This approach has got improvements in DFS and OS. Mucinous condition has been related to worse response to systemic chemotherapy but the evidence on this issue is weak. CHEMUCCA study arises to answer this question for mucinous colon cancer.

Objectives: To compare the disease free survival for stages II and III mucinous colon cancer who receive surgery plus systemic adjuvant chemotherapy vs. surgery alone.

Methods: Patient selection: A total of 1,134 patients were collected from a retrospective cohort diagnosed with high-risk stage II (505 patients) and stage III (629 patients) colorectal cancer between the years 2010 and 2021 aged from 18 to 75 years. Variables and analysis: The demographic variables analyzed are: age (years), sex (female/male), histology (non mucinous, mucinous), tumor differentiation grade (well, moderately or poorly differentiated), location (left, right, rectum), stage II high risk (tumor perforation, obstruction, LN< 12, perineural invasion, pT4), stage III (N1-2), molecular profile (KRAS, NRAS, BRAF mutation), systemic chemotherapy, MMR deficiency, DFS (months), OS (in months), time to recurrence and time to death. T student test and Kaplan Meier with log rank test analysis were used.

Results: Of 1,134 patients with colorectal disease in stage II high risk and III, 206 (18.17%) had mucinous histology and 928 (81.83%) had non-mucinous histology. 708 patients who received adjuvant chemotherapy, 129 (62.62%) in mucinous group and 579 (62.39%) in non mucinous group. Adjuvant systemic chemotherapy in mucinous colorectal cancer stage II and III including rectum improved the DFS p = 0.017. However, in a stratified analysis, patients with high risk stage mucinous colon cancer did not show any benefit with this approach (p = 0.056).

Conclusions: Adjuvant chemotherapy seems to be useful in mucinous colorectal cancer. This benefit could be diminished in mucinous high risk stage II colon cancer patients. It is worth to evaluate this patient’s sub-group in further analysis in order to recommend adjuvant chemotherapy.