Introduction

Hepatocellular carcinoma (HCC), accounting for >5 % of cancers globally, is ranked as the 6th most common cancer and the 3rd leading cause of cancer-related death worldwide. The incidence of HCC may continue increasing over the next 20 years and to peak around 2030 [1–3]. Etiologically, chronic hepatitis B (CHB) still remains the most common risk factor for HCC worldwide, however, after successful vaccination program against hepatitis B virus (HBV), chronic hepatitis C (CHC) has become an important cause of chronic liver diseases (CLDs) in both Western countries and the Asia–Pacific region. Nowadays, there are an estimated 170 million infected with hepatitis C virus (HCV) globally, and the incidence of HCC and HCV has increased in recent decades, suggesting an etiologic link. In Korea, about 10 % of cirrhosis and 12–17 % of HCC were due to HCV infection [1–3]. Even though the risk of transfusion-related HCV infection is almost zero in developed countries, infections via injection drug use and certain insanitary practices, such as acupuncture, tattooing, and body piercing, have become an emerging medical issue. HCC is a common cause of liver-related death among HCV-infected persons, developing predominantly in those with cirrhosis. Nevertheless, several studies have reported that HCC occurs in persons with bridging fibrosis without definite cirrhosis, although far less commonly [4–8]. To date, there are new insights into HCV-related hepatocarcinogenesis.

This article reviews hepatocarcinogenesis and measures for predicting and preventing the development of HCC in patients with chronic HCV infection.

Hepatocarcinogenesis in HCV

Since HCV lacks reverse transcriptase activity unlike HBV, it does not integrate into the host genome. Furthermore, as HCV is a completely cytoplasmic-replicating virus, the main hypothesis for carcinogenesis is that it occurs via indirect pathways through the effects of chronic inflammation, oxidative stress and subsequent hepatocellular injury. This assumption is supported by the fact that the presence of cirrhosis is almost a prerequisite for HCC development [9]. As a matter of fact, this is why patients with CHC are less likely to be candidates for hepatic resection in terms of preoperative liver functions and tumor locations, multiplicity, and invasiveness and have a higher cumulative recurrence rate, even after surgery, than those with CHB [10–12].

However, it is unlikely that necro-inflammation alone is sufficient to cause HCC. As a matter of fact, a significant minority arises in the absence of cirrhosis and other lines of evidence suggest that direct, virus-specific mechanisms may be involved [13, 14]. Recent studies have suggested that various HCV proteins, including the core, envelope, and nonstructural proteins, exert direct oncogenic effects by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses [13–15] (Fig. 1). HCV core protein, a 21-kDa nucleocapsid protein involved in binding viral RNA, is involved not only in viral particle assembly and generation of complete virions, but also in cell signalling, transcription activation, apoptosis, lipid metabolism and transformation [16, 17]. There are several hypotheses concerning its role in carcinogenesis [13, 18–22]. First, HCV core protein has been shown to induce reactive oxygen species even in the absence of inflammation. The oxidative stress may decrease metabolic processes within mitochondria, with a decline in microsomal triglyceride transfer protein activity, resulting in the development of steatosis [14, 23–26]. Second, it has also been shown to affect cellular regulatory pathways. For example, it can bind to p53 and pRb, tumor suppressor proteins and modulate the expression of p21/Waf, which is involved in cell cycle control, and interact with cytoplasmic signal transduction molecules to regulate transcription [16, 27]. More recently, HCV core protein seems to increase the serine phosphorylation of insulin receptor substrate (IRS)-1 and to activate c-Jun N-terminal kinase signaling and the proteasome activator 28γ, all of which are associated with insulin resistance [28–30]. Such hyperinsulinemia from insulin resistance—by its action on hepatic stellate cells, extracellular matrix, endothelial cells or connective growth factors—not only can accelerate the progression of fibrosis [31, 32], but also can increase accumulation of free fatty acids in the liver, leading to activation of some kinases, such as protein kinase C delta, inhibitor kappa B kinase, JNK, or mammalian target of rapamycin (mTOR) that are known to promote carcinogenesis [33, 34].

Fig. 1
figure 1

A schematic display of HCV-specific hepatocarcinogenesis. Various HCV proteins, including the core, nonstructural proteins (NS3, NS5A), and E2 exert direct oncogenic effects by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses. HCV hepatitis C virus, HCC hepatocellular carcinoma

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Apart from the core proteins, other HCV proteins have also been shown to contribute to hepatocarcinogenesis. For example, NS3 can promote hepatocarcinogenesis by its interaction with certain proteins, such as p21 and p53, whereas NS5A can also interact with cellular signalling components and regulatory protein kinases, leading to the suppression of the host immune response and inhibition of apoptosis [35–38]. Furthermore, the truncated form of HCV NS5A can become localized to the nucleus to act as a transcriptional activator. Besides, The E2 protein can interact with CD81 and inhibit T and NK cells, thereby promoting cell survival and proliferation.

Taken together, complex interactions of the various HCV proteins with host cell factors have also been shown to be sufficient to induce hepatocarcinogenesis, through alteration of cellular signaling cascades involved in cell metabolism and division [13, 14]. Overall, the synergism of indirect chronic inflammation and direct virus-host cell interactions are likely to determine the progression to HCC in patients with CHC.

How to predict HCC development?

As aforementioned, although HCV-specific hepatocarcinogenesis had been spotlighted recently, chronic inflammation and oxidative stress from immune responses against infected hepatocytes and resultant hepatic fibrosis still remain the major pathogenesis for development of HCC. Since such processes facilitate the accumulation of genetic alterations simultaneously, approximately half of cirrhotic nodules harbor chromosomal abnormalities and a loss of alleles [38]. Thus, an accurate assessment of overall fibrotic burden is an important prerequisite for risk stratification of HCC development.

Recently, liver stiffness (LS) measured noninvasively by transient elastography (TE) has been reported to be well correlated with histologically assessed liver fibrosis degree [39–43]. The principle of TE is based on the principle that the propagation velocity of a wave through a homogenous tissue is proportional to its elasticity, so livers with increasing degrees of scarring have decreasing elasticity and that a shear wave propagating through stiffer material would progress faster than in one with more elastic material [41, 44]. From this viewpoint, the role of TE for risk stratification of development of HCC have been evaluated to date [45, 46]. The first large prospective cohort study of 866 Japanese patients with CHC tested whether TE can predict the future development of HCC [45, 46]. During a mean follow-up of 3 years, 77 patients developed HCC. By multivariate analysis, together with age, male gender, and clinical cirrhosis, stratified TE value was identified as an independent risk factor for HCC development, with relative risks of 16.7, 20.0, 25.6, and 45.5 for TE values of 10–15, 15–20, 20–25, and >25 kPa, respectively, versus an TE value of <10 kPa as the reference and the cumulative incidence of HCC showed a step-wise increase according to stratified TE value. Interestingly, in this study, even patients with not so high level of TE (10–15 kPa) were still more subject to HCC development with an adjusted HR of 16.7, compared to those with a TE value <10 kPa. Overall, the fibrotic burden estimated by TE has shown the potential for a clinical role in predicting the development of HCC and, in part, demonstrated superior performance to histology and other noninvasive tools [47–52]. This is most likely due to the wider dynamic range of TE values in the evaluation of liver cirrhosis. In fact, as the stage of ‘‘cirrhosis’’ has to date been defined by histopathological evidence of one or two qualitative categories (METAVIR stage F4 or ISHAK S5–S6), or more generally by the presence of so-called ‘‘regenerative’’ or ‘‘cirrhotic nodules,’’ an interval scale cannot be used in this setting. However, the degree of liver fibrosis may vary widely among patients in this category, and the risk of HCC may not be uniform. Thus, in this regard, because TE value, expressed in kPa as a continuous variable, has a wide dynamic range within the cirrhotic stage from the cutoff level from non-cirrhosis (15–17 kPa) to the upper measurement limit of present devices (75 kPa), it would seem to be a more reasonable tool for detailed prognostication.

Prevention of development of HCC in patients with chronic HCV infection

The first prevention for HCV-associated HCC is avoidance of chronic HCV infection. However, unfortunately, vaccination against de novo HCV infection is currently not available, in contrast to HBV infection. Accordingly, the next step to reduce HCV-associated HCC is the effective eradication of HCV from the host using antiviral therapy from the viewpoint of the 2nd prevention. For several decades, interferon (IFN)-based therapy appears to be effective at both controlling HCV infection and reducing the risk of HCC [46]. Its preventive effect is the highest among patients who achieve sustained virologic response (SVR). A meta-analysis found that SVR was associated with a 79 % (95 % CI 0.73–0.84) reduction in the risk of development of HCC by patients with HCV-related cirrhosis. Such treatment to eradicate HCV is contributable to reduce hepatic fibrosis and cirrhosis, and prevention of HCC [53–55]. The cumulative incidences of HCC in treated and control patients with cirrhosis were 7.8 and 24.2 %, respectively (hazard ratio [HR], 0.45; 95 % confidence interval [CI], 0.24–0.83). Table 1 summarizes several RCTs where the risk of developing HCC had been reduced after successful antiviral therapy. A recent study suggested the additional benefit of IFN-based therapy among patients with cirrhosis even though they did not have a SVR to therapy. However, several large scaled randomized trials (HALT-C, COPILOT, and EPIC) have demonstrated that maintenance pegylated (PEG)-IFN fails to prevent HCC in patients with HCV-related cirrhosis among nonresponders. Lok et al. [56] reported that extended follow-up of the HALT-C Trial cohort for a median of 6.1 years showed a modest benefit of long-term PEG-IFN therapy in reducing the incidence of HCC in patients with hepatitis C and cirrhosis but not in those with advanced pre-cirrhotic fibrosis. HCV therapy has been revolutionized recently by development and approval of direct-acting antiviral agents (DAA), yielded by extensive researches of the crystal structure of several critical viral proteins [57–59]. In the year 2011, the first two DAAs, telaprevir (Incivek; Vertex Pharmaceuticals Cambridge, MA, USA) and boceprevir (Victrelis; Merck & Co Whitehouse Station, NJ, USA), both inhibiting the NS3/4A protease, had been approved for use in patients with chronic HCV infection with genotype 1 and marked the beginning of a new era in HCV therapy. Several clinical trials demonstrated that these two drugs were potent for the efficacy and safety in treatment-naïve genotype 1 HCV infection [60–62]. The addition of telaprevir and boceprevir to the standard PEG-IFN and ribavirin regimen has provided a major advance in the treatment-naïve and –experienced genotype 1 patients. Moreover, with the improvement of SVR rate with these new drugs, the rate of HCC development will be lower accordingly.

Table 1 Summary of randomized controlled trials on incidence of HCC among patients with HCV infection
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Although HCC has been treated curatively, such patients are still at risk of developing HCC in the future. As a matter of fact, more than half of the patients successfully treated with surgical resection experience recurrent HCCs within 5 years of surgery, despite successful resection. Therefore, for such “high-risk subjects”, so called the 3rd prevention might be beneficial. Recurrences should be differentiated into early and late recurrences. Early recurrences are the result of occult metastasis left behind after resection. Such tumors will usually become apparent within 2 years of surgery. In contrast, late or de novo recurrences are new, typically occurring more than 2 years after surgery, as the result of the underlying procarcinogenic liver disease, caused by cirrhosis itself or HCV. There have been several randomized controlled trials (RCTs) and at least one meta-analysis about effect of IFN therapy after resection of HCC, most of which consistently favors the use of IFN-based therapy [63, 64]. A meta-analysis by Singal et al. [63] showed that IFN-based therapy could reduce the risk of developing a new focus of HCC and that the benefit of IFN for HCC recurrence was stronger with SVR compared with non-responders [0.19 (0.06–0.60); P = 0.005]. However, notably, the benefit of antiviral therapy and SVR is primarily limited to prevention of late recurrence.

Taken together, since recent lines of evidence suggest the potential roles of virus-specific mechanisms [16, 17], the importance of an effective eradication of HCV from host can not be overestimated to reduce the risk of de novo development of HCC.

Management of HCC

Although surgical resection or local ablative therapies such as radiofrequency ablation (RFA) and percutaneous ethanol injection (PEI) achieve the best outcomes with a 5-year survival rate of 60–70 % in patients treated during early stages, only about 30 % are amenable to potentially curative treatments. Eventually, most patients are eligible for only palliative treatments in hope of prolonging life, and a multidisciplinary therapeutic approach is required for optimal treatment outcome. Nowadays, the molecular target agents have been spotlighted for several years. Sorafenib, an oral multikinase inhibitor blocking tumor cell proliferation and tumor angiogenesis by inhibiting serine/threonine kinase and several receptor tyrosine kinases such as vascular endothelial growth factor receptors (VEGFRs) 2 and 3, platelet-derived growth factor receptor-β, Fms-related tyrosine kinase (Flt), and c-kit had shown the proven survival benefits compared to the best supportive care through the two large trials [65–68].

In 2008, the SHARP trial in which 602 patients with advanced HCC were randomized to receive either sorafenib 400 mg b.i.d. (n = 299) or a placebo (n = 303) demonstrated that overall survival (OS) was significantly prolonged in sorafenib-treated patients compared with placebo group (10.7 vs. 7.9 months, respectively, p < 0.001) [65]. Furthermore, sorafenib significantly improved the time to disease progression (TTP) compared to placebo (5.5 vs. 2.8 months, respectively, p < 0.001). Following the SHARP trial, Cheng et al. [69] published a large-scale Asia–Pacific Phase III randomized trial of sorafenib versus placebo in 226 Asian patients (150 received sorafenib and 76 received placebo) from China, South Korea, and Taiwan study. This study had similar aims and design as the SHARP trial. The median OS was 6.5 vs. 4.2 months in the sorafenib and placebo groups, respectively (p = 0.014), whereas the median TTP was 2.8 vs. 1.4 months, respectively (p < 0.001). In this study, common drug-related adverse events included hand-foot skin reactions (45.0 %), diarrhea (25.5 %), alopecia (24.8 %), fatigue (20.1 %), rash or desquamation (20.1 %), hypertension (18.8 %), and anorexia (12.8 %). However, compared to the SHARP trial, more patients with hand-foot skin reactions and fewer with diarrhea were observed in the Asia–Pacific study [65, 69].

Notably, compared with the SHARP trial, the absolute median OS and TTP were shorter in the Asia–Pacific study, which might presumably have resulted from the difference in the baseline characteristics of enrolled subjects, suggesting the higher percentage of more advanced disease in the Asia–Pacific study. Similarly, a pilot study where 97 HCC patients with either main portal vein invasion or extrahepatic spread were treated with sorafenib demonstrated that the median TTP and OS were 2.2 and 7.7 months, respectively and that therapy was stopped due to adverse events or cost burden in 34 % of the patients [70]. Another Korean study also reported that the median TTP was 9.1 weeks [71]. The detailed differences between the two trials are summarized in Table 2.

Table 2 Comparison of the SHARP and Asia–Pacific trials
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Taken together, sorafenib became standard therapy for the treatment of advanced HCCin Asia as well as Western countries. However, the prognosis of HCC is generally worse than in Western countries. Furthermore, the high cost of sorafenib is an obstacle to its widespread use in clinical practice [69, 72–75]. Nevertheless, sorafenib has a firm position at the core of HCC therapy and its indications are anticipated to widen in the near future to intermediate HCC or as an adjuvant agent with or without a combination modality. A rational approach based on cost, quality of life, and survival will be urgently needed.

Besides, other small molecules, such as brivanib and erlotinib, and monoclonal antibodies, such as bevacizumab and cetuximab, are currently being studied in patients with HCC. Furthermore, the clinical implication of other conventional treatment modalities, including hepatic arterial infusion chemotherapy or localized concurrent chemoradiation therapy for advanced HCC, should be reilluminated in comparison with the novel molecular target agent and the combined methods should be considered to improve clinical outcomes [75, 76].

Conclusions

In Asia, a nationwide vaccination program would eventually decrease HBV-related HCC. Conversely, HCV infection has recently become a significant problem, leading to increase of HCV-related HCC. With the emerging importance of CHC as an etiology for CLDs, there is a pressing need for further research on HCV-associated carcinogenesis to identify the steps from chronic HCV infection to cancer, and that can help developing of prevention, early screening, and treatment. HCV-associated hepatocellular carcinogenesis should be clarified to provide insight into advanced therapeutic and preventive approaches for HCC, which will eventually decrease development of HCC risk and improved survival outcomes. Furthermore, continuous efforts have been put into finding new targets and molecular pathways for possible new drug development.