Design of Phase II Cancer Trials Using a Continuous Endpoint of Change in Tumor Size: Application to a Study of Sorafenib and Erlotinib in Non Small-Cell Lung Cancer

Abstract

The primary objective of phase II cancer clinical trials is to determine whether a new regimen has sufficient activity to warrant further study, with activity generally defined as tumor shrinkage. However, oncology drug development has been limited by high rates of failure (lack of efficacy) in subsequent phase III testing. This high failure rate may reflect the process by which antineoplastic agents are usually evaluated in phase II trials, i.e., via single-arm studies in which the primary efficacy measure is the proportion of patients who achieve a complete or partial response to the treatment. This design may efficiently eliminate truly ineffective therapy but may not reliably indicate whether subsequent phase III testing is warranted. We describe the design of a randomized phase II clinical trial of sorafenib in combination with erlotinib for the treatment of patients with non-small-cell lung cancer using change in tumor size, measured on a continuous scale, as the primary outcome variable. For the purpose of determining the sample size of the trial, we made assumptions as to the likely magnitude of treatment effect and the variability in tumor size changes based on data from four previous trials using these agents. The study design includes two different dosage arms and a placebo group with a total sample size of 150 patients and is powered to detect a modest reduction in the mean tumor size burden in the high-dose sorafenib arm compared with a slight increase in the placebo group. Clinical trial designs that treat change in tumor size as a continuous variable rather than categorizing the changes are feasible, and by inclusion of a prospective control group they offer advantages over conventional single-arm trials.