Perspectives on the design of clinical trials combining transarterial chemoembolization and molecular targeted therapy.

Transarterial chemoembolization (TACE) moderately prolongs the survival of patients with intermediate-stage hepatocellular carcinoma. Molecular targeted therapy (MTT) may improve the efficacy of TACE. However, the findings of clinical trials evaluating the efficacy of a combination of TACE and MTT are conflicting. We hypothesized that this disparity can be prevented using alternative study designs. In this review, we classify the pertinent issues of study designs into five domains: primary endpoints, patients, TACE procedures, timing of randomization, and drug administration. Furthermore, we discuss the methods for increasing the success rate by minimizing potentially confounding factors within these five domains. Transarterial chemoembolization (TACE) is the current standard therapy for patients with Barcelona Clinic Liver Cancer (BCLC) intermediate-stage hepatocellular carcinoma (HCC) [1, 2, 3]. The survival benefit of TACE is supported by the results of meta-analysis of clinical trials comparing TACE with other conservative treatments in patients with inoperable HCC [4]. The results showed that the median survival of patients improved from approximately 16 to 20 months following TACE [4, 5]. Although advances in TACE techniques and the use of new embolization agents may improve the efficacy of TACE [6, 7], other approaches are needed to further improve the outcome in HCC patients treated using TACE. Molecular targeted therapy (MTT) has improved the survival of patients with advanced-stage HCC [5, 8]. Therefore, combining MTT and TACE may additionally improve the survival in patients with intermediate-stage HCC. Many molecular targeted agents (MTA) are currently undergoing evaluation in randomized trials (table 1). However, the designs of these trials differ significantly. The results of two trials combining sorafenib and TACE were recently reported. Both trials failed to demonstrate a therapeutic benefit of the combination therapy for time to tumor progression (TTP) or overall survival (OS) [9, 10]. However, specific subgroups of patients who received treatment for more than 6 months exhibited significantly better survival (table 2). Because median survival can be greater than 2 years in patients with intermediate-stage HCC, it is likely that an extended exposure period is necessary for MTA effects to reach the biological threshold at which survival benefit becomes measurable. Therefore, early discontinuation of study drug treatment may significantly undermine the statistical power of efficacy analysis in randomized trials (fig. 1). Clinical trials should be designed to minimize confounding factors that could lead to early discontinuation of study drug [1, 2, 3, 11, 12]. Factors that are crucial in this regard can be categorized into five domains: (1) selection of primary endpoints, (2) selection of patient population, (3) selection of TACE procedures, (4) timing of randomization, and (5) study drug administration. In this review we discuss the confounding effects potentially associated with each domain and the possible interactions among domains in trials combining TACE and MTA. We also discuss strategies that can help improve sensitivity and accuracy measurements of MTA efficacy.