Adjuvant Chemotherapy for High-Risk Stage II Colon Cancer: A Population-Based Study

Background Adjuvant chemotherapy is recommended as an option for patients who have high-risk features. It remains unclear whether all patients with high-risk stage II colon cancer benefit from adjuvant therapy. The primary aim of this study is to evaluate the association between adjuvant chemotherapy and overall survival in patients with high-risk stage II colon cancer. Methods Utilizing the Surveillance, Epidemiology and End Results (SEER) database from 2010 to 2019, adult patients with high-risk stage II colon cancer defined as T4 tumor classification, perineural invasion, less than 12 lymph nodes harvested, and poorly differentiated histology. 1:1 ratio propensity matching was used to adjust for confounding variables. Survival differences based on receipt of adjuvant systemic therapy were summarized using a log rank test. Cox proportion hazard regression was used to evaluate overall survival. Results Of the 11,619 patients who met inclusion criteria, 2775 (24%) received adjuvant chemotherapy. Patients were more likely to receive adjuvant therapy if they were younger, married or partnered, or had left-sided lesions. Kaplan-Meier estimates showed an improvement in overall survival (log-rank test < 0.001). On pair-stratified Cox proportional hazards regression, adjuvant chemotherapy receipt was associated with 30% lower mortality hazard (hazard ratio [HR] 0.70; 95% CI 0.62, 0.80; p < 0.001). However, on landmark analysis, after excluding patients surviving < 3 months, adjuvant chemotherapy was no longer associated with mortality hazard (HR 0.90; 95% CI 0.79, 1.04; p = 0.144). Conclusion The findings from this large SEER database study provide support for not undergoing adjuvant chemotherapy to patients with high-risk stage II colon cancer.