Background: The effect of adjuvant chemotherapy on stage II colon cancer remains constantly controversial. Recently, however, several studies have reported the definite survival benefit of adjuvant chemotherapy (ACT) in T4 disease (stage IIB and IIC) among stage II colon cancer patients. The following study investigates the efficacy of ACT in patients with poorly differentiated stage IIA colon cancer. Methods: The first cohort of eligible patients (N=38384) diagnosed with stage IIA colon cancer was selected from the Surveillance, Epidemiology, and End Results database (SEER) between January 1, 2004, and December 31, 2010. Cox proportional hazards regression analyses and Kaplan-Meier curves were used to evaluate the survival benefit following ACT. Our findings were also evaluated in Fudan University Shanghai Cancer Center (FUSCC) cohort form FUSCC database. Results: In SEER cohort, poorly differentiated or undifferentiated tumor grade was associated with 21.5% increased cancer-specific mortality in patients who did not receive ACT (HR=1.215, 1.004-1.469, P=0.045, using poorly differentiated or undifferentiated ACT as a reference). In FUSCC cohort, poorly differentiated or undifferentiated tumor grade was also associated with increased DFS in patients who received ACT (HR = 0.160, 95% CI = 0.017-1.505, P=0.109, using poorly differentiated or undifferentiated, non-ACT as a reference). In addition, patients with poorly differentiated or undifferentiated tumor who did not receive ACT had a higher risk of distant metastasis and recurrence compared to patients who received ACT (log-rank P=0.027 and 0.119, respectively). Conclusion: ACT decreased the recurrence rate and distant metastasis rate thus improving prognosis for poorly differentiated or undifferentiated stage IIA colon cancer.
Keywords: adjuvant chemotherapy; stage IIA colon cancer; tumor grade.