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3519 Background: Tumor deposits (TDs) are isolated tumor foci in the pericolic, perirectal or mesocolic fat without residual lymph node (LN) tissue. TDs seem to impact the prognosis of stage III colon cancer (CC) patients (pts) but are only considered in TNM staging in the absence of LN metastases (LNM). We aimed at evaluating the prognosis value for disease free survival (DFS)of TDs in International Duration Evaluation of Adjuvant Chemotherapy (IDEA) France phase III study (NCT00958737) that compared 3 versus 6 months of adjuvant FOLFOX or CAPOX for stage III CC pts. Methods: All pathological reports of pts included in IDEA France trial were retrospectively analyzed. DFS according to the presence or absence of TDs was evaluated using Kaplan-Meier estimator. Multivariable Cox model analysis was performed to evaluate the association between TDs and DFS. This analysis did not included immunohistochemical biomarkers. Results: Among the 2022 pts included in IDEA France study, 1942 (96%) were analyzed. 80 pts were excluded: no pathological report (n = 68), pts without treatment (n = 12). TDs were found in 184 pts (9.47%), of whom 74 with N1a/b (40%), 55 with N1c (30%) and 55 with N2 LN stage (30%). All characteristics were similar according to the presence of TDs, except for tumor/node (TN) stage (T4 and/or N2 are more frequent in pts with TDs; p = .0046). The 3-year DFS rates were 65.59% [95% confidence interval (95%CI) 58.04-72.12] and 74.71% [95%CI 72.57-76.71] for pts with and without TDs, respectively (p = 0.0079). In multivariable analysis, TDs were associated with higher risk of recurrence or death (hazard ratio (HR) = 1.36, 95%CI 1.05-1.75, p = .0201), as well as T4 and/or N2 (HR = 2.21, 95%CI 1.03-1.59, p < .001), 3 months of adjuvant treatment (HR = 1.29, 95%CI 1.09-1.52, p = .0029), obstruction (HR = 1.28, 95%CI 1.03-1.59, p = .0233) and male (HR = 1.24, 95%CI 1.04-1.46, p = .0151). Adding TDs count to the LNM count, 35 out of 1454 N1a/b/c CC pts (2.4%) were reclassified as N2 and experienced worse 3 years DFS than confirmed N1 CC pts (p = .0151). Conclusions: TD is an independent and valuable prognostic factor for DFSin stage III CC pts and should be considered whatever the LNM status.