3606 Background: Mucinous adenocarcinoma (MC) is a histological subtype of colorectal cancer with ≥50% of mucinous component of tumor volume. According to WHO classification, tumor less than 50% of the lesion composed of mucin was considered as non-mucinous carcinoma (NMC).Mucinous histology has been shown to be an independent adverse prognostic factor in some studies, but not in others. However, prognostic implication of intermediate mucinous carcinoma (IMC) which had focal mucinous component <50% of tumor volume has not been studied yet. The aim of this study is to explore prognostic impact of IMC in patients with resected stage II or III colon cancer. Methods: This study involved 917 patients who underwent curative resection for stage II or III colon cancer in Severance Hospital, from 2003 to 2009. The proportion of mucinous component was reviewed and re-classified correctly by pathologists. MC was defined tumor having >50% mucinous component. Tumor with mucinous component but less than 50% regarded as IMC and less than 10% mucin as NMC. Results: Among 917 patients, 63 (6.9%) and 60 (6.5%) were MC and IMC, respectively. Median follow-up duration was 50.2 months (0.9~109.7) and Stage 3 was 48.1% (441/917). The similarities between MC and IMC were found as right colon dominant (MC: IMC: NMC = 60%: 67%: 34%, p<.001) and higher incidence of MSI-high compared to NMC (MC: IMC: NMC = 27%: 30%: 11%, p<.001). In stage III, the disease-free survival (DFS) rate at 5 years was 44% for MC, 56% for IMC, and 74% for NMC (p<.001). Subgroup analysis according to MSI status showed that DFS had significant inverse correlation with proportions of mucinous components in MSI-low or MSS group, but patients with MSI-high tumor showed higher five-year DFS rate (>85%) regardless of mucinous component. For stage II colon cancer patients, both mucinous histology and MSI had little clinical significance. Conclusions: In patients with curative resection for stage II or III colon cancer, IMC had similar characteristics to MC, which were right colon dominant and high incidence of MSI-high tumor. The prognostic impact of IMC was intermediate risk between MC and NMC in stage III patients with MSI-low or MSS tumor, but not in MSI-high group.