Long-Term Outcomes and Conditional Recurrence-Free Survival in Stage II Colon Cancer: The Impact of Surveillance and Recurrence Detection Strategies

Background: Adjuvant therapy decisions for T3N0 stage II colon cancer remain controversial. This study evaluates long-term outcomes, recurrence patterns, and conditional relapse-free survival (RFS) in pathologic T3N0 colon cancer. Methods: This retrospective study included 306 patients undergoing curative resection for T3N0 colonic adenocarcinoma (1995–2020). Early recurrence was defined as recurrence or death within 3 years after surgery. Survival was estimated via Kaplan–Meier. Cox regression, adjusted for treatment eras, evaluated survival factors. Inverse Probability of Treatment Weighting (IPTW) minimized selection bias. Conditional RFS utilized a 5-year landmark analysis. Results: Over a 133-month median follow-up, 72 patients (23.5%) recurred. Most recurrences (81.9%) occurred within 3 years; only 9.7% after 5 years. Five- and 10-year OS rates were 80.9% and 70.4%. Inadequate lymph node dissection (<12 nodes) was performed in 29.7% of the entire cohort and was found to be an independent adverse prognostic factor for OS. Adjuvant chemotherapy lacked overall OS benefit, though IPTW analysis suggested potential benefit in patients with inadequate dissection. Conditional RFS (5–10 years) for patients recurrence-free at 60 months was 95.0%. Exploratory analyses showed descriptive differences in post-relapse survival based on the clinical triggers prompting radiological evaluation (marker-triggered versus symptom-triggered presentations). Conclusions: T3N0 colon cancer recurrences occur predominantly within the first 3–5 years after surgery. Inadequate lymph node dissection is the primary adverse prognostic factor. Although a 5-year follow-up period appears adequate for most patients, individualized extended surveillance may be considered for selected high-risk patients. Adjuvant treatment and follow-up strategies should be tailored according to surgical quality and risk factors.