Predicting recurrence in patients with stage II and III colon cancer: Validation cohort and long-term follow-up of the experimental cohort.

215 Background: The prognosis of stage II and III colon cancer is heterogeneous and current staging system do not accurately predict recurrence. We previously reported a score that was able to select a subgroup of patient with excellent prognosis ( https://doi.org/10.1016/j.annonc.2022.04.177 ). Here we present long-term follow up of the experimental cohort and the results of the validation cohort. Methods: We included patients with pathologically confirmed diagnosis of stage II and III colon cancer at Hospital Universitario La Paz. The experimental cohort included patients from October 2016 to September 2020. The validation cohort included patients from October 2020 to August 2021. Our prognostic score assigns 1 point for each of the following features: T4, N2, R1 and high tumor budding. Patients with a score of 0 as compared to those with ≥1 had an excellent prognosis regardless AJCC TNM staging. We assess the time to recurrence (TTR) between both groups in the experimental and validation cohort. Results: Baseline characteristics of the experimental cohort (n = 304) were reported previously. 135 (44%) and 169 (56%) patients had a score of 0 and ≥1, respectively. After a median follow up of 45 months, 81 recurrences and 96 deaths were observed. Median TTR was not reached in either cohort (score 0 vs ≥1; P < 0.001), with a hazard ratio (HR) for recurrence of 0.13 [confidence interval (CI)95%: 0.05 to 0.32; P < 0.001]. At 24 months, 95% and 73% of the patients were recurrence free in the score 0 and ≥1 groups, respectively. Within the validation cohort (n = 86), thirty-eight (44%) patients had a score of 0 and 48 (56%) of ≥1. After a median follow up of 19 months, 14 recurrences were observed, all of them in patients with score ≥1. Mediant TTR was not reached in either cohort (P < 0.001), with a HR for recurrence of 0.14 (IC95%: 0.00 – 1.07, P = 0.05). At 12 months, 100% and 78% of the patients were recurrence-free in the score 0 and ≥1 groups, respectively. When assessing TTR according to AJCC TNM stage, we found similar TTR between patients with stage II (n = 45) and III (n = 41) (not reached in either cohort; P = 0.16), with a HR for recurrence of 0.47 (CI95%: 0.15 to 1.40; P = 0.17). At 12 months, 90% and 86% of the patients with stage II and III were recurrence-free. Conclusions: In this study, we validate a prognostic score that identifies a subgroup of patients with localized colon cancer with an excellent prognosis regardless of their TNM stage.