Efficacy of systemic Chemotherapy on high-risk stage II and III Mucnious colon cancer. CHEMUCCA study part I

Locally advanced colon cancer is a high-risk condition for tumour recurrence with poor survival. The current treatment is surgery followed by adjuvant chemotherapy based on fluoropyrimidines and oxaliplatin. This approach has improved the oncological outcomes on this population, however the mucinous condition has not been studied in depth and although the evidence is weak, it is thought to have a worse response to systemic chemotherapy. The CHEMUCCA study aims to answer this question. To evaluate the effectiveness of adjuvant systemic chemotherapy using the disease-free survival for stage II and III mucinous colon cancer who underwent surgical resection plus systemic adjuvant chemotherapy vs. surgery alone. Retrospective analytical study including patients diagnosed with high-risk stage II and stage III colon cancer, treated between 2010 and 2021, with a minimum follow-up of 3 years. Demographic variables and tumour features were analysed. The primary endpoint was disease-free survival. Log rank test and Cox regression were used. Of 1134 patients with high-risk stage II and III colon cancer disease, 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 the non-mucinous group. Adjuvant systemic chemotherapy in stage II and III mucinous colon cancer improved the DFS (HR = 0.58 [95 % CI 0.37−0.91]; p = 0,017). However, in a stratified analysis, patients with high-risk stage II mucinous colon cancer showed no benefit with this approach (HR = 0.4541 [95 % CI 0.19−1.03]; p = 0.06). Adjuvant chemotherapy has demonstrated to be effective in locally advanced mucinous colorectal cancer improving the oncological outcomes. However, this benefit could be diminished in high-risk stage II mucinous colon cancer patients. The administration of adjuvant chemotherapy on this patient's sub-group must be balanced according to risk versus benefits.