Continual reassessment methods in phase I trials of the combination of two drugs in oncology.

Most phase I trials in oncology use standard methods for treating successive groups of patients with increasing doses in order to determine the maximum tolerated dose (MTD). These methods have been criticized because they treat many patients at suboptimal dose levels, and do not provide an accurate estimation of the best dose level. Continual reassessment methods for the study of toxicity in single agent phase I trials have recently been advocated since they present many advantages over traditional methods. Although the advantages of these methods are recognized by most clinical investigators, their use is not widespread and their advantages have not yet been universally accepted. A maximum likelihood continual reassessment method was conducted retrospectively and compared to the originally planned standard method in a two drug combination phase I trial in order to study its applicability in this setting. Calculations from the binomial distributions and simulations were used for identifying the MTD, for the proportion of patients treated at the MTD or at one dose level just below, and for the proportion of patients treated at doses above the MTD. If the new method had been applied in this study, the MTD would have been reached much earlier, since, most of the time, higher dose levels were recommended. This result shows the feasibility of the new method in a two-drug setting and its use should be encouraged since fewer patients are treated at suboptimal dose levels or at dose levels above the MTD.