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Sorafenib, HCC treatment: Where do we go from here?
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Hepatology Early View May 2010
Abby B. Siegel *, Sonja K. Olsen, Arthur Magun, Robert S. Brown Jr
Departments of Medicine and Surgery, Columbia University College of Physicians and Surgeons, New York, NY
email: Abby B. Siegel (aas54@columbia.edu)
*Correspondence to Abby B. Siegel, Center for Liver Disease and Transplantation, NewYork-Presbyterian Hospital, 622 West 168th Street, PH 14 105-C, New York, NY 10032-3784
Summary: There are several challenges facing the hepatology, transplant, and oncological community in the treatment of HCC. First, additional work is required to clarify the molecular pathogenesis of HCC and identify key targets for therapeutic intervention. The development of sorafenib underscores the potential for targeting additional receptors and other mediators in oncogenic pathways.
Second, we need to ensure that various therapies are studied in combination with each other and also in succession. Specifically, the role of sorafenib as adjunctive therapy needs to be evaluated both before and after surgery and with locoregional therapies.
Third, study design needs to be critically evaluated, particularly in the age of molecular therapies. As discussed previously, the American Association for the Study of Liver Diseases has recently convened a panel of multidisciplinary experts to comment on the design of clinical trials for HCC. This group suggested that randomized phase II trials designed to determine the antitumor activity of a particular agent be encouraged and that the time to progression, not the response rate, might be a more useful endpoint in these trials. This thinking is underscored by data showing that survival advantages can be seen in the absence of large tumor response rates and that response rates may not capture the benefit of a molecular therapy as they would with an intervention such as chemoembolization or radiofrequency ablation.[17]
Finally, because transplantation remains the primary method of treating HCC and the underlying liver disease in the West, every effort needs to be made to streamline the process of referring eligible HCC patients to transplant centers.[78]
Further study must also focus on identifying predictive and prognostic biomarkers to guide our use of this new armamentarium against HCC. In addition to improved treatment modalities, improved methods for HCC surveillance in at-risk populations are critically important. Despite their deficiencies, surveillance programs have been proven to improve survival in those with HCC.
The treatment of HCC is complicated by the wide variety of underlying liver diseases associated with the development of this tumor as well as the various therapeutic modalities available to patients. The identification of sorafenib and the survival benefit that it confers to patients with unresectable HCC represents a new era in the treatment of HCC. Studies are underway to assess additional molecular targets and to determine optimal combinations and sequencing of treatment modalities to maximize patient outcome in this new, rapidly shifting landscape.
Abstract
The approval of sorafenib as the first effective drug for the treatment of hepatocellular carcinoma (HCC) represents a milestone in the treatment of this disease. A better understanding of HCC pathogenesis has led to the development of several novel targeted treatments. HCC is treated in a uniquely multidisciplinary way requiring surgeons, hepatologists, interventional radiologists, and oncologists. This review describes the molecular pathogenesis of HCC, explores current and future treatments based on these pathways, and describes how these new therapies may augment existing approaches to HCC treatment.
Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related deaths.[1] HCC usually occurs in the setting of underlying liver diseases, including hepatitis B and C, nonalcoholic fatty liver disease, and alcohol-induced cirrhosis. The incidence of HCC in the United States has almost doubled in recent decades because of the increased prevalence of chronic hepatitis C, migration from endemic areas, and, increasingly, nonalcoholic fatty liver disease.[2][3] Until recently, there were no systemic treatment options that clearly improved survival for those with advanced HCC. Because of the diverse etiologies underlying HCC, there is likely no one genetic mutation or molecular pathway crucial for all HCC tumorigenesis.
The vast majority of HCC cases develop in the setting of chronic hepatitis or cirrhosis and may take over 30 years to develop. Initially, hepatocytes proliferate in the setting of increased levels of cytokines such as tumor necrosis factor a. Genetic and epigenetic changes then lead to dysplastic hepatocytes and finally HCC.[4] Hepatitis B may act as a direct carcinogen by integrating into the host genome and leading to genomic instability. Cirrhosis is not always a necessary intermediate, and patients may have excellent underlying liver function; this leads to different treatment possibilities (e.g., the resection of large tumors). Hepatitis C virus (HCV) infection is almost always associated with cirrhosis when HCC has developed. Both cirrhosis and HCV may act on different pathways to enhance cancer development. For instance, HCV has been shown to act as a Wnt ligand, which can up-regulate cell signaling pathways, whereas cirrhosis leads to many changes, including oxidative stress, which may contribute to carcinogenesis.[5] HCC is a particularly heterogeneous disease, and many pathogenic processes contribute to carcinogenesis. However, several carcinogenic pathways have now been identified in the development and progression of HCC, and they provide new molecular targets for HCC treatment (Fig. 1).
We summarize several promising targets and drugs that affect these pathways, including the vascular endothelial growth factor receptor (VEGFR), epidermal growth factor receptor (EGFR), and mammalian target of rapamycin (mTOR) pathways. We discuss ways to conceptualize combining these agents alone and with various other treatment modalities, including locoregional therapies, resection, and transplantation. We discuss novel pathways involving fibroblast growth factor receptor (FGFR), insulin-like growth factor receptor (IGFR) signaling, and modulation of apoptosis. Finally, we examine how molecular studies in HCC are helping to define new targets for HCC treatment and prevention.
Abbreviations
AFP, alpha-fetoprotein; AKT, protein kinase B; c-MET, mesenchymal epithelial transition factor; CP, Child-Pugh; DCE, dynamic contrast-enhanced; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; FGFR, fibroblast growth factor receptor; GEMOX, gemcitabine and oxaliplatin; HCC, hepatocellular carcinoma; HCV, hepatitis C virus; HDAC, histone deacetylase; HER, human epidermal growth factor receptor; IGF, insulin growth factor; IGF1R, insulin-like growth factor 1 receptor; IGFR, insulin-like growth factor receptor; MEK, mitogen-activated protein kinase kinase; MRI, magnetic resonance imaging; mTOR, mammalian target of rapamycin; PDGFR, platelet-derived growth factor receptor; PI3K, phosphoinositide 3-kinase; SHARP, Sorafenib HCC Assessment Randomized Protocol; SRC, sarcoma; TRAIL, tumor necrosis factor-related apoptosis-inducing ligand; ULN, upper limit of normal; VEGF, vascular endothelial growth factor; VEGFR, vascular endothelial growth factor receptor.
VEGFR/EGFR Pathway
VEGFR.
HCC is one of the most vascular solid tumors known. Vascular endothelial growth factor (VEGF) is a primary mediator of angiogenesis in HCC.[6][7] Antiangiogenic drugs such as sorafenib (which acts in part by blocking the VEGF tyrosine kinase receptor) and bevacizumab have already shown significant clinical activity in HCC, and sorafenib is now the first Food and Drug Administration-approved agent for patients with advanced HCC.[8][9]
Sorafenib is a tyrosine kinase inhibitor directed against several targets, including VEGFR2 and Raf kinase. It has now been studied in two large, multicenter, randomized controlled trials in patients with advanced, unresectable HCC. In the Sorafenib HCC Assessment Randomized Protocol (SHARP) study, 602 primarily European patients were randomized to sorafenib (400 mg twice daily) or placebo. Patients with advanced disease in this study were defined as being ineligible for, or having disease progression after, surgical or locoregional therapies. They also had an Eastern Cooperative Oncology Group performance status of 2 or less, and Child-Pugh (CP) liver function class A disease. The sorafenib group had a median overall survival time of 10.7 months versus 7.9 months in the placebo arm (P 0.001).[9]
In a second randomized study conducted in Asia, 271 patients were again randomized to sorafenib or placebo. The median survival time in the sorafenib group was 6.5 months versus 4.2 months for the placebo group (hazard ratio = 0.68, P = 0.014).[10] This worsened survival may have been due to more advanced disease on presentation, but the degree of benefit from sorafenib in each study was almost identical. The results of these studies led to the approval of sorafenib for treatment of advanced HCC in patients in the United States and Europe in 2007. These trials both demonstrated a clear overall survival advantage in the setting of a randomized controlled trial, the endpoint with the highest level of evidence to support it.
Overall, sorafenib is usually well tolerated. Major side effects include hand-foot syndrome (5%-8% in the US study and 11% in the Asian study), fatigue (8%-10%), and diarrhea (9%). Although there was no significant increase in serious bleeding events seen in either of the phase III trials, this complication may develop more commonly in patients with CP class B or C disease.[11]
These two pivotal trials of sorafenib both studied patients with preserved liver function. Less is known about the drug's effects in patients with decompensated liver disease, although sorafenib is approved in the United States for everyone with unresectable HCC. Abou-Alfa and colleagues[12] looked at the use of sorafenib in a phase II study of 137 patients, 39 of whom had CP class B disease, and found no difference in the tolerability of sorafenib in patients with CP class A or B disease. A retrospective study evaluated sorafenib in 59 patients, 23 of whom were classified as having CP class B disease and 10 of whom had CP class C disease. The median survival times for patients with CP class A, B, and C disease were 8.3, 4.3, and 1.5 months, respectively (P = 0.0001). The authors concluded that there was no benefit from systemic therapy in patients with very advanced liver disease.[11] Subsequently published work has suggested that the dosage of sorafenib should be reduced to 200 mg twice daily in patients with bilirubin levels >1.5 times but <3 times the upper limit of normal (ULN); for patients with levels 3 times ULN but less than 10 times ULN, even 200 mg every 3 days was not tolerated.[13] The use of sorafenib in patients with decompensated liver disease needs to be studied prospectively in larger numbers of patients to better assess its efficacy.
To date, few predictive biomarkers have been shown to definitively correlate with the response to sorafenib. Expression of phosphorylated extracellular signal-regulated kinase by immunohistochemistry was associated with improved progression-free survival in a subset of patients treated in a phase II trial of sorafenib in HCC.[12] These data were validated in abstract form in the SHARP trial.[14] Several biomarkers are being actively studied, including circulating endothelial cells and plasma cytokines, but none has yet shown definite predictive or prognostic value. Imaging studies using dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) have shown that decreased angiogenesis is at least one mechanism of efficacy for sorafenib, but the relative contributions of blockading the other pathways is unknown.[15] As we move forward with using sorafenib in HCC, defining mechanisms of action and biomarkers that predict response will be crucial for developing individualized and cost-effective care.
Bevacizumab is a recombinant humanized monoclonal antibody directed against VEGF-A. It is approved for the treatment of several malignancies in the Unites States, including non-small cell lung cancer, breast cancer, kidney cancer, and colon cancer. Bevacizumab's mechanism of action may include normalization of leaky tumor vasculature in addition to the reduction of the actual number of blood vessels seen within tumors.[16] Bevacizumab has been studied as a single agent in the treatment of HCC. In a multicenter phase II study of 46 patients with compensated liver disease and unresectable HCC, we reported 6-month progression-free survival in 65% of patients, with 13% experiencing a partial response to treatment (a 30% decrease in the sum of the longest diameters of the target lesions). This response rate compares favorably to that seen in the sorafenib trials, in which only 2% to 3% of patients had objective radiological responses. The criteria for advanced disease in this trial differed from those in the SHARP trial. Patients in our study were excluded if they had greater than 50% involvement of the liver parenchyma by a tumor, invasion of the main portal vein or vena cava, or extrahepatic disease. On the other hand, 26% of the patients in the bevacizumab study had CP class B disease. The study was powered for a primary endpoint of 6-month progression-free survival of 60%, which it met; the median progression-free survival time with bevacizumab was 6.9 months, and the overall survival rate was 53% at 1 year. A major side effect of bevacizumab was bleeding, with 11% of patients having serious bleeding complications, including one fatal variceal bleed early in the study. After modifying the protocol to perform upper endoscopy and banding of esophageal varices prior to using bevacizumab, we no longer saw this complication.[8] It is possible that we saw more serious bleeding events because more of our patients had CP class B disease, in contrast to the pivotal sorafenib trials discussed, in which almost all patients had CP class A disease.
Issues related to heterogeneous patient selection in HCC trials have now been discussed as part of an American Association for the Study of Liver Diseases conference in 2006, and guidelines were published in 2008.[17] These guidelines call for standardization of populations studied with novel targeted therapies, and suggest the use of the Barcelona Clinic Liver Cancer criteria to define advanced disease. The conference participants also discussed standardization of clinical endpoints; they moved away from the response rate as a primary measure of outcome and suggested randomized phase II trials with a time to event endpoint as one way of moving forward in clinical trials in HCC with less potential selection bias.[17]
Bevacizumab has also been studied in conjunction with chemotherapy for the treatment of unresectable HCC. In a phase II study of 33 patients, almost half of whom had metastatic disease, treatment with bevacizumab and gemcitabine and oxaliplatin (GEMOX) resulted in a 20% response rate with an overall median survival time of 9.6 months.[18] In a phase II trial of GEMOX alone, a response rate of 18% was seen in HCC, and this suggested little clinical benefit with the addition of bevacizumab.[19]
Sunitinib is another oral tyrosine kinase inhibitor that blocks several receptors, including VEGFR1, VEGFR2, VEGFR3, platelet-derived growth factor receptor a(PDGFRa), PDGFRbeta, and stem cell factor receptor (KIT). Like sorafenib, it is approved for the treatment of another particularly vascular tumor, renal cell carcinoma. Its clinical spectrum overlaps that of sorafenib, and it has been studied in two separate phase II trials in HCC using different dose schedules.[20][21] The first study by Zhu and colleagues[20] showed a response rate of 2.9% in 34 patients, with an average overall survival time of 9.8 months. Their primary outcome was progression-free survival. The dosage was 37.5 mg daily for 28 days followed by 14 days of rest in 6-week cycles. The authors found that higher levels of inflammatory biomarkers such as interleukin-6 predicted worsened outcome, and DCE MRI imaging could predict delayed recurrence. Faivre and colleagues[21] studied a higher dose of sunitinib, 50 mg daily for 4 weeks followed by a 2-week rest, in 37 patients from France and Asia. The primary outcome, the response rate, was at 2.7%, and toxicity was high with this dose schedule, with 10% of patients dying from treatment-related causes. There is currently an ongoing international phase III trial comparing sorafenib with sunitinib in advanced HCC patients.
EGFR.
EGFR is an active target for several oncological chemotherapeutics. The receptor may be attacked extracellularly through the use of antibodies that block the receptor or intracellularly via binding to the adenosine triphosphate binding site of the receptor's tyrosine kinase domain. Cetuximab and panitumumab are antibodies targeted against EGFR, and they are used for the treatment of advanced colorectal cancer and head and neck cancers.[22-24] Gefitinib and erlotinib target the EGFR tyrosine kinase, and are used in the treatment of lung and pancreatic cancers.[25][26] EGFR is overexpressed in 40% to 70% of HCCs,[27] and activation of the receptor is also involved in HCC pathogenesis.[28][29] Fluorescence in situ hybridization showed extra EGFR gene copies in about half of HCCs in one study, and this was accompanied by gains in chromosome 7, which suggested balanced polysomy rather than gene amplification.[27] EGFR inhibitors prevent the development of HCC in animal models,[28][30] and tyrosine kinase inhibitors against EGFR have shown some activity in HCC to date.
Erlotinib is an orally administered small molecule EGFR inhibitor that targets the tyrosine kinase domain. It has been studied as a single agent in HCC in two US phase II trials at a dose of 150 mg daily. In one study of 38 patients with unresectable HCC, 8% of patients had partial responses, 32% were progression-free at 6 months, and the median overall survival time was 13 months.[31] Erlotinib was studied in another trial of 40 patients with Child A or B cirrhosis and advanced HCC. In this trial, there were no complete or partial responses, with a median overall survival time of 10.8 months.[32] Recently, Thomas and colleagues[33] evaluated the combination of erlotinib with bevacizumab in a phase II study of 40 patients. With progression-free survival as the primary outcome, the combination yielded a 25% objective response rate with a provocative median overall survival time of 15.6 months. Patients in this study were slightly less advanced in terms of Barcelona Clinic Liver Cancer staging than those in the SHARP trial, although more had CP class B disease, and more were previously treated. Side effects of this regimen included gastrointestinal bleeding (12.5%) and fatigue (20%). This combination is currently being compared to sorafenib in a multicenter phase II trial.
In contrast to erlotinib, cetuximab is a monoclonal antibody directed against the epidermal growth factor (EGF) receptor. Like bevacizumab, it has become an important component of standard therapy for many patients with advanced, K-ras wild-type colorectal cancer. Unlike erlotinib, it has not shown evidence of significant tumor responses in HCC. In one phase II trial, it was given to 30 patients with unresectable HCC for a period of 6 weeks. Although the regimen was well tolerated, no objective tumor responses were seen.[34] In 45 treatment-naïve patients with advanced HCC, the combination of GEMOX with cetuximab was associated with progression-free survival of 4.7 months, overall survival of 9.5 months, and a 40% 1-year survival rate.[35] Given the efficacy of the GEMOX combination without the additional agent, the benefit of cetuximab remains uncertain. Similarly, lapatinib, a dual tyrosine kinase inhibitor against EGFR and human epidermal growth factor receptor 2 (HER2; another member of the EGFR family and an important target for breast and gastric cancer treatment), did not show significant activity in a multicenter phase II trial.[36]
Unfortunately, no specific biological predictors of response to EGF antagonists have been found to date for HCC patients. Specific activating mutations of EGFR have been found in lung cancer and have been shown to predict response to some EGFR tyrosine kinase inhibitors,[25] but they have not been seen in HCC.[37] Similarly, although K-ras mutations have predicted insensitivity to EGFR blockade in several tumor types, these also have not yet been well studied in HCC.[38] Interestingly, development of a skin rash has been shown to predict response to all inhibitors of the EGFR pathway, and there is a suggestion that this may also be the case in HCC.[31]
mTOR Pathway
The EGF and insulin growth factor (IGF) signaling pathways activate several downstream proteins, including phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mTOR. AKT is an oncogene that regulates several processes, including cell growth via the mTOR pathway. In one large study, aberrant mTOR signaling was seen in about half of HCC cases, and this was associated with insulin-like growth factor and EGF activation. Blockage of mTOR signaling in a cell culture and a xenograft model with everolimus decreased tumor growth.[39]
Sirolimus (rapamycin) is an mTOR inhibitor with immunosuppressive properties that may be used in solid organ transplant patients. It has recently been demonstrated to have antitumor properties via inhibition of m-TOR signaling.[40-42] In a retrospective study of 73 patients who underwent liver transplantation for HCC outside the Milan criteria, those who received sirolimus had better survival than those who were given tacrolimus-based immunosuppression, and this was thought to be due to later and possibly fewer recurrences.[43] The use of sirolimus is associated with an increased risk of hepatic artery thrombosis and poor wound healing, primarily in the immediate posttransplant period, and this limits its use as initial immunosuppression.
Sirolimus has also been studied outside transplantation in patients with primary liver tumors. For instance, in a small pilot study of 21 patients with HCC, 6 patients either had stable disease or had a partial remission.[44] Further studies need to be performed to assess the role of sirolimus in the treatment of HCC in both pretransplant and posttransplant settings. Everolimus is another mTOR inhibitor that has been shown to have activity against HCC in xenografts and is now being studied in phase II trials in metastatic disease.[45] Everolimus has also been studied in conjunction with sorafenib treatment with promising early results.[46]
New Directions
The identification of sorafenib marks a major advance in the field as the first effective targeted therapy for HCC. Sorafenib is now approved for the treatment of advanced HCC in the United States and Europe, and its role in treatment is being studied in different contexts. For instance, it is being evaluated as adjuvant and neoadjuvant therapy in patients undergoing locoregional treatment and as adjuvant therapy in patients undergoing surgical resection. Our institution is pilot-testing sorafenib in high-risk HCC patients (i.e., patients defined as being outside the Milan criteria or having aggressive features on explant pathology) after transplantation to assess safety in this setting. There is also consideration of its use as a chemopreventive in patients with cirrhosis. The patient numbers and resources needed to complete such a trial would be large, however, and there are also concerns about possible long-term toxicities, such as squamous cell carcinoma, which has been reported with sorafenib use and may possibly be related to the hyperkeratosis that is a side effect of the drug.[47]
In addition to evaluating sorafenib in these different contexts, there are several ways to conceptualize HCC therapy for advanced disease. First, there is broad interest in evaluating existing drugs that affect other pathogenic pathways and comparing these directly to sorafenib. Second, studies are underway that are evaluating vertical blockade, in which the same pathway is interrupted at different points by, for example, bevacizumab (an antibody to VEGF) and sorafenib (a small molecule tyrosine kinase inhibitor against VEGFR). The idea of targeting the same pathway at several levels is appealing because it may lead to more complete blockade, block feedback loops, and have nonoverlapping resistance patterns.[48] Horizontal blockade, in contrast, refers to the use of different drugs that interrupt different signaling pathways, such as bevacizumab with erlotinib, which targets EGFR. Many of these combinations have preclinical evidence of synergy and/or block proposed resistance pathways seen in one of the drugs.[49] Additionally, blockade at different pathways may provide fewer overlapping toxicities. Combinations of sorafenib with chemotherapy are also being investigated, with an intergroup trial in the United States studying doxorubicin with sorafenib on the basis of phase II data.[50]
It is not clear which of these conceptualizations of treatment will be more effective or whether consecutive sequencing of drugs will provide better efficacy in comparison with giving drugs simultaneously. Because of the importance of angiogenic signaling in HCC, it may be that more complete blockade of this pathway will be particularly beneficial. There are data from a phase I study using sorafenib and bevacizumab together that show a promising response rate of 59%, but at the cost of significant toxicity, including hand-foot syndrome, hypertension, and diarrhea.[51] This combination is currently being studied in a National Cancer Institute-sponsored trial in HCC. It is also known that responses can be seen through the sequential use of a VEGFR tyrosine kinase inhibitor after the failure of other antiangiogenic drugs in renal cell carcinoma, and this raises the question whether survival might be the same as (or better than) that with simultaneous drug treatment with less toxicity.[52][53]
Data for the horizontal approach with targeted therapies, although it is appealing conceptually, have been mixed so far in other cancer types. For instance, a single-arm phase II trial using bevacizumab and erlotinib in renal cell carcinoma looked promising, but a subsequent randomized phase II trial of bevacizumab with or without erlotinib in this disease showed no significant clinical benefit with the addition of erlotinib.[54][55] In colorectal cancer, two large randomized trials used combinations of bevacizumab and anti-EGFR antibodies and showed significant toxicity and worsened outcomes in patients treated with both targeted agents simultaneously.[56][57] In contrast, sequencing these antibodies has been shown to provide clear survival benefits in patients with metastatic colon cancer.[58] The phase II trial performed in HCC with bevacizumab and erlotinib is encouraging, however, and has been expanded into a larger multicenter study. A careful evaluation of all these paradigms - vertical blockade, horizontal blockade, and sequential therapies - is needed to determine which options provide the best outcomes. These options will likely differ according to the goals of therapy. For instance, in a patient who may be able to be downstaged prior to resection or transplantation, a rapid response rate may be the most important endpoint, whereas for a metastatic patient, prolonged survival with minimal toxicity may warrant different treatment options.
New pathways are increasingly being examined as possible targets for HCC treatment. These include resistance pathways, apoptotic pathways, signal transduction pathways, and cell cycle pathways. One potentially promising approach involves targeting the FGFR pathway, which is thought to play a role in resistance to VEGF blockade.[59] Brivanib alanate is a dual inhibitor of VEGFR and FGFR tyrosine kinases. Brivanib has shown preclinical activity in animal models[60] and has shown preliminary evidence of activity in HCC patients who have progressed on previous antiangiogenic therapy.[61] To test this hypothesis clinically, a large randomized phase III trial is being conducted in which brivanib is being studied as second-line therapy in HCC patients who have progressed on sorafenib.
Apoptosis pathways are also attractive targets for modulation in anticancer therapies. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) initiates apoptosis by joining two death receptors, death receptor 4 and death receptor 5. Akazawa and colleagues[62] have shown that in malignant liver cell lines, death receptor 5 undergoes endocytosis with trafficking to lysosomes and allows protease release into the cytosol and apoptosis. There are currently trials underway that are using different TRAIL agonists with sorafenib in HCC.
There is also a great deal of interest in examining the IGFR inhibitors in HCC. Features of metabolic syndrome, including diabetes, obesity, and insulin resistance, are related to both HCC development and mortality, and dysregulation of the IGF axis is seen in all of these disorders.[63][64] Preclinical studies suggest that blockade of the IGFR receptors block HCC cell growth, and at least 30% to 40% of HCCs overexpress insulin-like growth factor 1 receptor (IGF1R).[65-67] Culture models suggest that HCC cells may overcome IGF1R via up-regulation of HER3, the main ligand of EGFR, and this suggests the possible synergistic effects of blocking both targets.[67] Several companies are developing IGF receptor antibodies, and phase II trials using these drugs in HCC are currently ongoing. Table 1 shows some of the targeted molecular therapies currently being tested in HCC.
Molecular Studies in HCC and the Role of Inflammation
Currently, there is no single molecular framework for classifying all HCC, but much work is underway to determine molecular predictors of outcome and response to therapies. Using HCC samples, Lee and Thorgeirsson[68] reported initial array data, clustering tumors into two categories based on survival. They found that genes associated with antiapoptosis and cell proliferation were more prevalent in tumors of patients with poorer survival. They then found that HCCs with phenotypic markers of hepatic progenitor cells also had a worsened prognosis.[69]
Hoshida and colleagues[70] have attempted to create unifying molecular subclasses of HCC incorporating both biological and clinical criteria. The group collected eight publicly available gene expression data sets and identified three robust subclasses of HCC. The first subclass was associated with higher rates of recurrence and more vascular invasion; molecularly, these tumors exhibited activation of WNT signaling pathways. Subclass 2 tumors were larger than the others, had the highest alpha-fetoprotein (AFP) levels, and often exhibited AKT activation. Subclass 3 tumors tended to be smaller and were associated with a good survival signature. Studies such as these point the way toward novel targets for therapy and also better selection of specific therapies for subtypes of HCC.
By examining gene expression in liver tissue surrounding tumors, Hoshida and colleagues[71][72] were able to show an association between a 132-gene profile, late recurrence of tumors, and survival. This argues for a field effect and predicts that those with a more inflammatory underlying liver are more prone to develop second primaries (confirmed genetically to be different than the primary tumors).
Finally, molecular markers are also being examined as possible predictors of response to therapy. Ji and colleagues[73] investigated micro-RNA patterns in 455 resected HCC patients and found that expression of micro-RNA 26 was both predictive and prognostic, with lower expression being associated with response to interferon in the adjuvant setting but lower overall survival. Expression of this micro-RNA was also linked to inflammatory signaling cascades.
Inflammatory signaling pathways also play a role in HCC development and may ultimately yield chemoprevention opportunities. For instance, Haybaeck and colleagues[74] found that the inflammatory cytokines lymphotoxin and lymphotoxin induced inflammation and HCC in a mouse model, and inhibition of the lymphotoxin receptor in a transgenic mouse model suppressed HCC formation. These data raise the question whether antilymphotoxin agents (which are already being studied in rheumatoid arthritis) may be examined in the future as chemopreventives in patients at risk for HCC.[75]
Novel Predictive and Prognostic Biomarkers
In addition to identifying molecular subtypes of HCC, noninvasive biomarkers such as imaging technologies and plasma markers that will not require tissue for analysis will be crucial for tailoring HCC treatment. Functional imaging is one attractive way of assessing the overall prognosis and response to therapy. Rather than evaluating the response on the basis of tumor diameters, the European Association for the Study of the Liver criteria have been proposed for assessing enhancement patterns of clinical responses from treatment rather than just tumor sizes.[76] Similarly, for antiangiogenic agents, DCE MRI has been studied as a correlate of tumor response.[8][20] All of these modalities require further study, standardization, and validation.
Other peripheral biomarkers are beginning to be evaluated as predictors of outcome. Chan and colleagues[77] evaluated serum AFP levels in 188 patients randomized to either doxorubicin or a combination of older chemotherapies called PIAF (doxorubicin, cisplatin, 5-FU, and interferon alpha). They found that of 117 patients who had elevated AFP levels (>20 ug/L), 47 patients had an AFP response defined as a >20% decrease in AFP after two cycles of chemotherapy. An AFP response was independently associated with overall survival in a multivariable model. It is unclear whether the AFP response will be useful as a predictive or prognostic marker for novel targeted therapies.[77] Similarly, plasma biomarkers such as VEGF, fibroblast growth factor, interleukin-6, and circulating endothelial cells are being studied as novel biomarkers of response to antiangiogenic drugs. To date, none of these has been conclusively validated.
Summary
There are several challenges facing the hepatology, transplant, and oncological community in the treatment of HCC. First, additional work is required to clarify the molecular pathogenesis of HCC and identify key targets for therapeutic intervention. The development of sorafenib underscores the potential for targeting additional receptors and other mediators in oncogenic pathways.
Second, we need to ensure that various therapies are studied in combination with each other and also in succession. Specifically, the role of sorafenib as adjunctive therapy needs to be evaluated both before and after surgery and with locoregional therapies.
Third, study design needs to be critically evaluated, particularly in the age of molecular therapies. As discussed previously, the American Association for the Study of Liver Diseases has recently convened a panel of multidisciplinary experts to comment on the design of clinical trials for HCC. This group suggested that randomized phase II trials designed to determine the antitumor activity of a particular agent be encouraged and that the time to progression, not the response rate, might be a more useful endpoint in these trials. This thinking is underscored by data showing that survival advantages can be seen in the absence of large tumor response rates and that response rates may not capture the benefit of a molecular therapy as they would with an intervention such as chemoembolization or radiofrequency ablation.[17]
Finally, because transplantation remains the primary method of treating HCC and the underlying liver disease in the West, every effort needs to be made to streamline the process of referring eligible HCC patients to transplant centers.[78]
Further study must also focus on identifying predictive and prognostic biomarkers to guide our use of this new armamentarium against HCC. In addition to improved treatment modalities, improved methods for HCC surveillance in at-risk populations are critically important. Despite their deficiencies, surveillance programs have been proven to improve survival in those with HCC.
The treatment of HCC is complicated by the wide variety of underlying liver diseases associated with the development of this tumor as well as the various therapeutic modalities available to patients. The identification of sorafenib and the survival benefit that it confers to patients with unresectable HCC represents a new era in the treatment of HCC. Studies are underway to assess additional molecular targets and to determine optimal combinations and sequencing of treatment modalities to maximize patient outcome in this new, rapidly shifting landscape.
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