Introduction: Clinical trials in hepatocellular carcinoma (HCC) exhibit a high degree of heterogeneity. These heterogeneities may lead to unexpected results among clinical trials. Area covered: In this review, we address the heterogeneity noted in early phase HCC trials, trials involving transarterial chemoembolization, and advanced HCC trials. Furthermore, we discuss possible methods to attenuate the detrimental effects of heterogeneity when conducting clinical trials. Expert opinion: Clinical trials in HCC exhibit an inherently high degree of heterogeneity because of various reasons: tumor heterogeneity, different cirrhotic backgrounds, various etiologies of cirrhosis, and geographical differences in practice and expertise. Such heterogeneity may cause imbalance among the enrolled patient population, premature withdrawal from the clinical trial, and variable response to the treatment. In addition, methodological heterogeneity also exists in designing trial protocol and response evaluation. All these factors may eventually lead to conflicting results among clinical trials. Accounting for these heterogeneities is important to foster the success of future trials. In recent years, significant progress with molecular targeted agents and immune checkpoint inhibitors was made in advanced HCC. These new agents are also being tested in clinical trials involving earlier stage HCC and will also face the challenge of these issues.
Keywords: Clinical trial; hepatocellular carcinoma; heterogeneity; trial design.