Impact of Adjuvant Chemotherapy on Overall Survival in Early‐Onset Stage II‐III Mucinous Adenocarcinoma of The Colon: A Propensity‐Based Analysis

BACKGROUND: Incidence of early-onset colon cancer is rising. Younger patients often present with advanced disease and distinct molecular profiles. Mucinous adenocarcinoma (MAC) represents a biologically unique subtype that may demonstrate limited responsiveness to adjuvant chemotherapy (AC). This study evaluated association between AC and overall survival (OS) in patients with early-onset stage II and III MAC. METHODS: Patients aged < 50 years diagnosed with stage II-III MAC were identified from NCDB (2006-2020). Stage II was categorized as high- or low-risk, with high-risk defined by presence of ≥ 1 of: < 12 lymph nodes retrieved, lymphovascular/perineural invasion, poor differentiation, or pT4 disease. Stabilized inverse probability of treatment weighting, Kaplan-Meier analysis, and multivariable Cox regression were performed to assess the association between AC and OS. RESULTS: Among 3333 patients, 42.9% were stage II and 57.1% stage III. AC was administered to 70.1% of patients, including 41.3% with stage II and 91.7% with stage III disease. AC was not associated with improved OS in either high-risk or low-risk stage II subgroups but was significantly associated with improved OS in stage III disease (HR 0.71, 95% CI 0.54-0.93). CONCLUSION: AC was associated with improved survival in stage III but not stage II early-onset MAC, including those with high-risk features.