Evidence for cure by adjuvant therapy in colon cancer: observations based on individual patient data from 20,898 patients on 18 randomized trials.

PURPOSE: Limited data are available on the time course of treatment failures (recurrence and/or death), the nature and duration of adjuvant treatment benefit, and long-term recurrence rates in patients with resected stage II and III colon cancer.

METHODS: The data set assembled by the Adjuvant Colon Cancer Endpoints Group, a collection of individual patient data from 18 trials and more than 20,800 patients testing fluorouracil-based adjuvant therapy in patients with stage II or III colon cancer, was analyzed.

RESULTS: A significant overall survival (OS) benefit of adjuvant therapy was consistent over the 8-year follow-up period. The risk of recurrence in patients treated with adjuvant chemotherapy never exceeds that of control patients, signifying that adjuvant therapy cures some patients, as opposed to delaying recurrence. After 5 years, recurrence rates were less than 1.5% per year, and after 8 years, they were less than 0.5% per year. Significant disease-free survival (DFS) benefit from adjuvant chemotherapy was observed in the first 2 years. After 2 years, DFS rates in treated and control patients were not significantly different, and after 4 years, no trend toward benefit was demonstrated. This benefit was primarily driven by patients with stage III disease.

CONCLUSION: Adjuvant chemotherapy provides significant DFS benefit, primarily by reducing the recurrence rate, within the first 2 years of adjuvant therapy with some benefit in years 3 to 4, translating into long-term OS benefit. This reflects the curative role of chemotherapy in the adjuvant setting. After 5 years, recurrence rates in patients treated on clinical trials are low, and after 8 years, they are minimal; thus, long-term follow-up for recurrence is of little value.