P-279 Adjuvant chemotherapy for patients with stage III colon cancer, three months vs six months. A single centre experience

The duration of adjuvant treatment in stage III colon cancer remains under continuing debate. Based on the results of the MOSAIC studies and the IDEA analysis, the possibility of proposing 3-month adjuvant treatment is assessed, with CAPOX being the choice, in low-risk groups (T1-3, N0-1) and thus limit the Oxaliplatin toxicity, while the recommendation for the high-risk group (T4/N2) is stable, the best option continues to be six months of treatment. This is a retrospective observational study. We included all patients had received adjuvant chemotherapy platino-based in Hospital Universitario La Paz from October 2016 to December 2021. Follow-up has been carried out until December 2022. High-risk tumours are defined as T4 and/or N2, Low-risk tumours T1-3/N0-1. Disease-free survival (DFS) is defined as the time from diagnosis to relapse or death. Overall survival (OS) is defined as the time from diagnosis to death or last contact. Survival was estimated with the Kaplan-Meier method and statistical analysis with long- rank test and cox-proportional hazards model. A total of 180 patients have received platinum-based adjuvant chemotherapy. Forty patients have received 3 months of chemotherapy (3C) and 140 patients six months (6C). The median age at diagnosis was 64.68 (IQR 58.09-71.97) median 64.89 (IQR 60.47-70.10) in group 3C and 64.84 (IQR 57.10-72.31) in 6C. The overall median follow-up was 22.9 months (IQR 14.63-42.57). During the follow-up 28 disease-free survival events (15.6%) have occurred and 12 (6.7%) of death events without documentations of recurrence happened. The median DFS was 19.08 months (IQR 12.13-37.51) 17.82 months (IQR 8.28-30.69) in 3C and 19.32 months in 6C (IQR 12.99-39.50). There were not significant differences between both groups (p: 0.81). Six patients (15%) in 3C group relapsed with a median 5.92 months (IQR 5-7.53) and 22 patients (15,71%) in 6C, median 13.73 months (IQR 9.44-20.57), HR 0.97 (95% IC 0.78-1.22, p=0.81). The median OS was 22.85 months (IQR 14.63-42.09), 18.92 months (IQR 13.81-30.77) in 3C and 30.28 months in 6C (IQR 14.78-43.17), with significant statistical difference (p=0.02). Five patients (12.5%) in 3C have died with a median 4.13 months (IQR 3.37-9.40) and seven patients (5%) in 6C, median 32.73 months (IQR 31.33-36.57). HR for OS comparing 3C vs 6C was 0.73 (95% IC 0.55-0.97, p= 0.03). An analysis by subgroups has been carried out, based on risks groups. The median OS of high-risk group was 21.83 months (IQR 14.12-41.75), 18.27 months (IQR 10.42-22.78) in 3C vs 23.55 months (IQR 14.54-41.80) in 6C, with significant statistical difference (p < 0.005). HR 0.59 (95% IC: 0.44-0.8, p= 0.0006). On the contrary, in the low-risk group, the median OS was 29.13 (IQR 15.37-43.37), 19.60 months (IQR 14.70-30.80) in 3C vs 33.48 (IQR 17.27-47.43) in 6C, was barely missed the statistical significance (p=0.58). There is no evidence of clear benefit by systematically shortening the duration of adjuvant therapy in stage III colorectal cancer. In our setting, three months adjuvant chemotherapy could be considered in low-risk group.