The objective of this study is to conduct a pooled analysis of National Surgical Adjuvant Breast and Bowel Project (NSABP) colon trials involving surgery and surgery plus 5-fluorouracil and leucovorin (5-FU/LV) to compare survival and establish a baseline from which to evaluate future studies.

All patients enrolled in NSABP adjuvant trials C-01 through C-05 with stage II and III disease who were treated with surgery or with surgery plus 5-FU/LV were examined for overall survival (OS), disease-free survival (DFS), and recurrence-free interval (RFI). Time-to-event by treatment group was examined using adjusted Kaplan–Meier estimates and multivariable Cox regression analysis.

There were 2,966 eligible patients: 693 (23%) surgery and 2,273 (77%) surgery plus 5-FU/LV; 1,255 (42%) stage II and 1,711 (58%) stage III. Age ≥60 years [hazard ratio (HR) = 1.36, P < 0.0001], male gender (HR = 1.20, P = 0.0012), and more nodes positive or fewer nodes examined (P < 0.0001) were associated with worse survival. At 5 years, the adjusted OS was 0.62 [confidence interval (CI) = 0.60–0.63] in the surgery group and 0.76 (CI = 0.74–0.78) in the surgery plus 5-FU/LV group. Treatment with 5-FU/LV was associated with improved outcome compared with surgery: OS (HR = 0.62, P < 0.0001), DFS (HR = 0.66, P < 0.0001) and RFI (HR = 0.64, P < 0.0001). Improved OS with adjuvant treatment was seen in both stage II (HR = 0.58, 95% CI = 0.48–0.71) and stage III disease (HR = 0.65, 95% CI = 0.55–0.75).

This analysis demonstrates that treatment of colon cancer patients with 5-FU/LV following surgery provides benefit over surgery alone and can provide anticipated survival outcomes with which to compare modern adjuvant trials.