Left-sided colon cancer (LSCC) and right-sided colon cancer (RSCC) have shown distinct clinical and prognostic features. We investigated the effect of adjuvant chemotherapy (ACT) on cause-specific survival (CSS) in patients with stage II LSCC and RSCC.

Using the Surveillance, Epidemiology and End Results (SEER) database, a cohort of patients with stage II colon cancer, aged between 20 and 49 years was identified. Both Cox proportional hazards regression and Kaplan-Meier survival analysis as well as propensity score matching were used.

Overall, 5633 patients were eligible. Patients with RSCC were more likely to be male, black, and younger, with a poor grade and histologic type, and were more likely to have more regional nodes examined and larger tumor size. After propensity score matching, CSS was significantly superior in patients with RSCC compared to those with LSCC (Hazard Ratio (HR): 0.80, 95% CI: 0.68-0.95, P=0.01). However, no survival benefit was observed for patients with LSCC after ACT (HR: 1.10, 95% CI: 0.90-1.35, P=0.35), and surprisingly, ACT was found to do more harm than good in patients with RSCC (HR: 1.31, 95% CI: 1.05-1.63, P=0.02). Even among patients with high-risk features such as T4 stage and regional nodes examined<12 in both groups, ACT still did not improve CSS except for T4 stage LSCC (HR: 0.65, 95% CI: 0.44-0.97, P=0.02).

The results of this analysis indicate that the prognosis of RSCC is better than that of LSCC in stage II colon cancer, and ACT did not improve CSS in patients with either LSCC or RSCC. Even in patients with parts of high-risk features, ACT still did not improve CSS, except for T4 stage LSCC.