408 Background: Fluoropyrimidine-based adjuvant chemotherapy is a standard treatment option for patients with high risk II or stage III CRC. It is, however, unclear if a subset of patients will benefit from chemotherapy more than others. MiR21, a small non-coding RNA, has been associated with promotion of tumor cell growth and metastasis. To assess the effect of miR21 on chemotherapy, we analyzed the association of miR21 expression with clinical outcomes and known prognostic factors. Methods: MicroRNA detection was performed by in situ hybridization on a CRC tissue microarray containing specimens from 130 cases (stage I, 21 patients; II: 44; III: 33; IV: 32). MiR21 expression was graded as negative (no staining in all tissue cores), low (0-10% staining), moderate (20-40%) and strong (50-100%), and was analyzed with stage, grade, expression of VEGF, Ki67, LEF1, OPN and MSH2 by immunohistochemistry. Cox proportional hazards regression analysis was performed to assess the association of miR21 expression with 10-year recurrence-free survival in the subgroup of 77 stage II or III patients. Results: In all, miR21 expression had moderate positive correlation with genes associated with tissue proliferation and invasion, including Ki67 (Spearman's r=0.42, p<0.001), VEGF (r=0.32, p<0.001) and OPN (r=0.32, p<0.001), and weak correlation with LEF1 (r=0.22, p=0.012) and MSH 2 (r=0.18, p=0.039). In the subgroup of 36 patients treated with adjuvant therapy, low or negative miR21 expression (≤10%, n=15) was associated with increased recurrence (HR =3.5; p=0.05). In the multivariate Cox regression model including stage, grade and LEF1 expression, the association of low or negative miR21 with cancer recurrence remained significant along with grade and LEF1. Ki67 was excluded from the multivariate model because of significant association with miR21 (r=0.44, p=0.007) in the analyzed group. Conclusions: Our results suggest that low miRNA21 expression is associated with increased risk for recurrence in CRC patients received adjuvant chemotherapy. Further investigation of miR21 in randomized studies is warranted to establish its role as a predictor for CRC in the setting of adjuvant therapy.