The role of tyrosine kinase inhibitors in hepatocellular carcinoma
Since the approval of the multityrosine kinase inhibitor (TKI) sorafenib (Nexavar, Bayer and Onyx) as the standard of care for intermediate to advanced stages of hepatocellular carcinoma (HCC), there has been considerable interest in developing more potent TKIs to improve morbidity and mortality for patients with HCC. Much of the research on TKIs targets pathways implicated in angiogenesis, given that HCC is a highly vascularized cancer type. It was theorized that the efficacy of sorafenib is primarily attributable to its angiogenesis targets-namely, vascular endothelial growth factor receptors, platelet-derived growth factor receptors, FLT-3, and RAF kinases. Over the past 2 years, several pivotal phase 3 trials of newer TKIs targeting similar pathways have failed to meet criteria for superiority or noninferiority to sorafenib. Reasons for this may stem from the genetic and biologic heterogeneity of HCC. Genomic studies of tumor samples have shown scarce uniformity in kinase mutations, underscoring the variability that exists in HCC. This beckons the question of whether efforts should shift to other potential targets, either within the realm of TKIs or other targets entirely. Receptor tyrosine kinases, such as those encoded by the MET proto-oncogene, are expressed in certain individuals and have shown to be susceptible to targeted TKIs. As researchers continue to investigate therapies, the goal is to further research efforts into culprit oncogenes that mediate tumor progression, which will likely lead to more personalized and targeted regimens.