Impact of adjuvant chemotherapy on recurrence risk in stage II colon cancer.

Abstract

533 Background: Although clinical guidelines recommend consideration of adjuvant chemotherapy in high-risk stage II colon cancer, the impact on recurrence risk and cancer related survival is unclear. Furthermore, among Medicare patients, adjuvant chemotherapy was not associated with improved survival. We examine the effect of adjuvant chemotherapy on recurrence risk and overall survival in a diverse cohort. Methods: 6,095 patients who underwent surgery for stage II-III colon cancer (2006-2007) were randomly selected from facilities reporting to the National Cancer Data Base for additional abstraction of tumor information, 5 year recurrence and survival. Death or second cancer within 6 months were excluded. Patients were classified as high or low risk using standard pathologic factors. Multivariate Cox regression with propensity score weighting was performed to compare recurrence risk and overall survival. Results: Of 3,423 patients with stage II colon cancer, 26.9% (n = 883) received chemotherapy compared to 76.2% (n = 1,839) of stage III patients. Among stage II patients, 47.8% (n = 1,636) had at least one high risk feature and 30.8% (n = 481) of these received chemotherapy. Five year recurrence rate in stage II patients was 13% (n = 392), greater in high risk compared to non-high risk patients (13.3% vs 9.3% p < 0.0001) and 24.4% (n = 874) in stage III patients. Chemotherapy did not improve recurrence risk in stage II patients regardless of risk status (High risk: hazard ratio [HR] 1.37; 95% CI 0.96 - 1.97; Non-high risk: HR 1.39; 95% CI 0.91 - 2.11). Chemotherapy was associated with a significant improvement in recurrence risk in stage III patients (HR 0.79; 95% CI 0.63 - 0.96). However, chemotherapy was associated with improved overall survival in both high (HR 0.69; 95% CI 0.51 - 0.92) and non-high risk stage II patients (HR 0.76; 95% CI 0.55 - 1.04), and also in stage III patients (HR 0.47; 95% CI 0.41 - 0.54). Conclusions: Adjuvant chemotherapy was not associated with a lower recurrence rate among stage II colon cancer patients. The observed survival benefit associated with chemotherapy is likely attributable to non-oncologic factors such as patient selection. Decision-making regarding chemotherapy use in this cohort should be carefully approached.