Association of modern era adjuvant chemotherapy with improved survival in patients with stage II colon cancer.

Abstract

671 Background: Patients are often selected for adjuvant therapy after resection of stage II colon cancer based on the presence of poor risk factors. However, the survival advantage of chemotherapy in this population is unclear and there remains variation in clinical practice. Methods: The National Cancer Data Base was analyzed for colon cancer patients treated 1998-2006. The primary outcome was OS between patients who did or did not receive adjuvant chemotherapy. Additional stratification variables included high-risk disease features, age, multi-agent chemotherapy, and diagnosis after 2004 when oxaliplatin was approved for adjuvant therapy. Demographic and disease information was compared using the Pearson Chi-squared test and binary logistic regression, effect size with Cramer's V/Phi for categorical variables, and survival data with Cox regression. Propensity score weighting was utilized to account for the possibility of selection bias. Results: Of 1,078,091 patients with colorectal cancer, 153,110 stage II colon cancer patients met inclusion criteria. Mean age was 72, 46% were male, 84% stage IIA (AJCC 6thed.), 9% stage IIB, and 20% received adjuvant chemotherapy. Predictors of receiving treatment included age<65, male gender, community treatment facility, geographical location, non-Medicare insurance, education level, and diagnosis before 2004. All patient sub-groups analyzed experienced improved OS with adjuvant chemotherapy regardless of the number of high-risk features, age, multi-agent chemotherapy, or adjustment for covariates. Median OS was 13.2 years in the chemotherapy group and 7.0 years in the no-chemotherapy group (p< 0.001). Median and 5-year OS was improved in both high and low-risk patients who received chemotherapy compared to those who did not with a median follow-up >5 years. Conclusions: This large-scale study with long-term follow-up demonstrated that adjuvant chemotherapy was associated with a clinically relevant improvement in OS regardless of treatment regimen, patient age, or high-risk features in patients with resected stage II colon cancer. The results of this retrospective analysis warrant further investigation in prospective trials.