The role of 5-fluorouracil dose in the adjuvant therapy of colorectal cancer

Abstract

In many centres, the use of 5-fluorouracil (5-FU) combined with levamisole has become standard therapy for the treatment of patients with Dukes' C colon cancer. However, the role of levamisole remains unclear. All of the published adjuvant studies for colorectal cancer in which 5-FU (either as a single agent or in combination with other cytotoxics or levamisole) was compared to a no-treatment control group were ranked according to the total planned dose of 5-FU (assuming a body weight of 70 kg or a body surface area of 1.7 m2) over a three-month time frame. The effect of planned total dose of adjuvant therapy on the reduction of mortality was analysed using indirect comparisons of dose on the log odds ratio of death in a linear regression analysis. Overall, this analysis demonstrated a significant reduction in the odds of death for those receiving 5-FU regimens compared to untreated controls (estimate 0.82, 95% CI 0.74 to 0.91, p < 0.001). This effect was larger in those receiving a larger planned dose; for a total dose of 5-FU in the first three months of greater than 10 grams, 8 to 10 grams, less than 8 grams or oral 5-FU, estimates were 0.71, 0.79, 0.93 and 1.04, respectively (p = 0.02 for trend). Similar results were observed when the planned total dose of 5-FU received over 12 months was analysed. The analysis was then repeated by separating those studies in which 5-FU and levamisole were compared to a no-treatment control. A larger effect was seen in the 5-FU/levamisole trials (odds ratio, 0.64) compared to the other 5-FU regimens (odds ratio 0.86, p = 0.04). However, when adjusted for dose, the effect of levamisole was no longer significant (p = 0.09). These data suggest two separate hypotheses. The first is that the benefit associated with the use of 5-FU and levamisole given as adjuvant therapy in Dukes' C colon cancer is directly related to the planned total dose of 5-FU administered. Alternatively, in view of the fact that levamisole was part of the treatment regimens in two of the three studies in which the total planned dose of 5-FU exceeded 10 grams in three months (or 40 grams in 12 months), levamisole may be critical to outcome and the 5-FU total dose or dose intensity less relevant.