Efficacy of adjuvant fluorouracil and leucovorin in stage B2 and C colon cancer. International Multicenter Pooled Analysis of Colon Cancer Trials Investigators.

The International Multicenter Pooled Analysis of Colon Cancer Trials (IMPACT) investigators have now completed two large systematic reviews of adjuvant therapy trials in colon cancer. The IMPACT 1 study pooled data from three separate trials each comparing the efficacy of 5-fluorouracil (5-FU)/leucovorin with observation alone as adjuvant treatment for 1,526 patients with Dukes' B or C colon cancer. The results showed that treatment with 5-FU/leucovorin significantly reduced mortality by 22% (P = .029) and events such as relapse, second tumor, or death by 35% (P < .0001) after 3 years of follow-up. The side effects associated with 5-FU/leucovorin were clinically acceptable. The IMPACT 1 study also showed a clear benefit of adjuvant treatment for patients with Dukes' C colon cancer, but not for stage-B patients. After up to 10 years of follow-up, 5-FU/leucovorin significantly reduced mortality by 30% for patients with Dukes' C disease (P = .003), but only reduced mortality by 8% in patients with Dukes' B colon cancer (P = .658). The aim of the IMPACT 2 study was to determine whether 5-FU/leucovorin is an effective adjuvant treatment for patients with Dukes' B2 colon cancer. Results were pooled from five separate trials that randomized 1,016 patients. After a median of 5.75 years of follow-up, B2 patients receiving 5-FU/leucovorin did not have a significant increase in overall survival or event-free survival. At 5 years, the hazard ratio for overall survival was 0.86 (90% confidence interval, 0.68 to 1.07) and for event-free survival was 0.83 (90% confidence interval, 0.72 to 1.07). 5-Fluorouracil/leucovorin was not recommended as a standard adjuvant treatment for all patients with Dukes' B2 colon cancer.