Introduction

Hepatocellular carcinoma (HCC) is a very common form of cancer that is typically associated with a poor prognosis. Indeed, worldwide, HCC is the third most common cause of cancer death, as well as being the fifth most frequent cancer in men and the seventh most frequent cancer in women [1], [2]. HCC is particularly common in Asian countries and sub-Saharan Africa, where 80% of worldwide cases occur [1], [3]. However, there is concerning evidence suggesting that the incidence of HCC is increasing in a number of Western countries [1], [4]. Unfortunately, more than 80% of HCC patients present with advanced disease. The treatment options available to these patients are limited and the prognosis is poor [5].

A number of different treatment approaches are available for HCC. Surgical tumor resection is the gold standard of treatment of HCC in patients who do not have advanced disease or extensive comorbidities (including cirrhosis). However, as already noted, most patients are diagnosed with advanced HCC and are therefore not candidates for resection [1], [6]. Liver transplantation is another potentially curative treatment option for HCC, but, similar to surgical resection, is limited to a relatively small proportion of patients [1], [6]. Loco-regional therapies, such as percutaneous ablation and radiofrequency, arterial chemoembolization, and conventional chemotherapies appear to offer limited survival benefits in most cases [1], [6], [7]. Clearly, alternative treatment options are needed.

With our increased understanding of the molecular mechanisms underlying cancer, specific molecular targeted therapies have been developed. One of the key molecular mechanisms underlying HCC is thought to be increased tumor angiogenesis caused by heightened vascular endothelial growth factor (VEGF) signalling [8], [9]. As such, sorafenib, a multikinase inhibitor that blocks VEGF signaling, has been approved for treatment of HCC [1], [6]. This agent has been found to significantly improve time to progression and median survival time compared with placebo in patients with advanced HCC [10], [11]. However, these improvements appear to be relatively modest (approximately three months) [9]. Therefore, other drugs targeting the molecular mechanisms underlying HCC continue to be investigated.

Bevacizumab, a humanized monoclonal antibody that binds VEGF-A [12], been approved for the treatment of various cancers and is currently under investigation as a treatment for HCC [9]. Although the precise mechanism of action is incompletely understood, bevacizumab is thought to decrease tumor vascularity and growth by directly binding with VEGF [13]. This in turn prevents VEGF binding with its receptor and the initiation of the associated angiogenic signal cascade. Bevacizumab may also help normalize tumor vasculature, improving oxygenation and the delivery of cytotoxic drugs [14]. At present, bevacizumab is an accepted treatment for several cancers, notably colorectal, non-small-cell lung, and metastatic breast cancer [13]. A number of Phase II clinical trials have investigated bevacizumab as a treatment for advanced HCC [9]. To date, however, there have been no Phase III trials conducted examining the efficacy and safety of bevacizumab (alone or in combination with other agents) for the treatment of this disease. To gain a better understanding of the efficacy and safety of bevacizumab for the treatment of advanced HCC, we performed a systematic review of the literature reporting findings from relevant Phase II clinical trials.

Materials and Methods

Results

Selection of Trials

A total of 26 potentially relevant trials were identified in the literature search (Figure 1). After review of the titles, six of these records were found to be duplicates and were excluded. The abstracts of the remaining 20 records were reviewed and a further eight were excluded, including seven meeting abstracts. The remaining 12 records underwent full-text review for assessment of eligibility. A total of eight trials [15]–[22] met the eligibility criteria and were included in the systematic review.

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Figure 1. Flow diagram of study selection.

https://doi.org/10.1371/journal.pone.0049717.g001

Patient Characteristics

A total of 300 patients were included in the eight trials (Table 1). The number of patients from individual trials ranged from 10 to 59. All patients had advanced HCC that was unresectable and/or not amenable to loco-regional therapy. For the trials that reported CLIP scores (five of eight trials) [15], [16], [18], [19], 20% to 60% of patients had scores of 3 or 4. For the trials that reported BCLC stages (four of eight trials) [16], [18]–[20], a high proportion (65% to 90%) of patients had stage C cancer. A total of five trials reported on the severity of liver disease using the Child-Pugh classification system [17]–[21]. The majority of patients (58% to 100%) had Child-Pugh class A severity of disease, indicating well-compensated disease. Except for 2 (5%) patients in the trial reported by Sun et al. who had Child-Pugh class C severity [17], the remaining patients had Child-Pugh class B severity of disease. Six of eight trials reported ECOG Performance Status [15], [17], [19]–[22]. The vast majority (95% to 100%) of patients had ECOG scores of 0 or 1, and no patient had a score greater than 2. The proportion of patients with underlying HBV varied considerably, ranging from 7% to 80%. The proportion of patients with underlying HCV was similarly variable, ranging from 0% to 60%.

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Table 1. Characteristics of trials and patients.

https://doi.org/10.1371/journal.pone.0049717.t001

Treatment Regimens

Bevacizumab was given as first or second line treatment in all but two [20], [22] trials (Table 1). Bevacizumab was given in combination with erlotinib in four of the eight trials [18]–[21] (Table 2). Bevacizumab was given as a monotherapy in only one trial [15] and was given in combination with capecitabine [16], capecitabine+oxaliplatin [17], or gemcitabine+oxaliplatin [22] in the remaining trials. Bevacizumab was most commonly administered at a dose of 10 mg/kg [15], [18]–[22]. However, a dose of 5 mg/kg was given in two trials [15], [17] and a dose of 7 mg/kg was given in one trial [16]. Dosing typically occurred on day 1 of the dosing cycle (14–21 days) [15]–[18], [20], but occurred on days 1 and 15 in three studies involving 28 day cycles [19], [21], [22]. There was variation in the number of treatment cycles between trials, ranging from a median of 2 cycles to 15 cycles (Table 1). Most trials [16]–[22], however, involved a median of 2 to 6 treatment cycles.

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Table 2. Summary of efficacy (N = 300 patients).

https://doi.org/10.1371/journal.pone.0049717.t002

Toxicities

All trials reported on the toxicities experienced during bevacizumab therapy (Table 3). The more common toxicities (experienced by ≥20% of patients, all grades) included nausea and/or vomiting (54%), fatigue (53%), any hemorrhage (46%), diarrhea (44%), increased aspartate transaminase/alanine transaminase (38%), anorexia (37%), dry skin (30%), epistaxis (29%), acne (27%), mucositis (21%), and hypertension (20%). Most toxicities were grade 1 or 2. The most common grade 3 or 4 toxicities (experienced by ≥5% of patients) were increased aspartate transaminase/alanine transaminase (13%), fatigue (12%), hypertension (10%), hemorrhage (8%), diarrhea (8%), and neutropenia (5%).

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Table 3. Summary of toxicities (N = 8 studies; N = 300 patients).

https://doi.org/10.1371/journal.pone.0049717.t003

Gastrointestinal (GI) bleeding was experienced by a total of 30 patients (grade 1/2 = 18, grade 3/4 = 12) in seven of the eight trials [15]–[20], [22]. Esophageal varices were a commonly reported source of GI bleeding [15]–[19], [22]. Two patients who experienced GI bleeding in the trial reported by Thomas et al. [19] had known portal hypertension.

A total of five patient deaths were reported. In the trial reported by Sun et al. [17], one patient died due to gastric perforation with sepsis. This death was considered secondary to cirrhosis and esophageal varices, but was reported as being probably related treatment. In the trial reported by Siegel et al. [15], one patient died due to treatment-related variceal bleeding. In the trial reported by Zhu et al. [22], one patient died due to respiratory failure. This death was considered possibly related to the gemcitabine and/or oxaliplatin given in combination with bevacizumab. In the trial reported by Thomas et al. [19], one patient died due to complications after experiencing GI bleeding. This patient had known portal hypertension. In the trial reported by Philip et al. [21], one patient died of respiratory failed caused by pneumonia. This death was considered to be unrelated to treatment.

Noted toxicity-related reasons for patient withdrawal included GI bleeding (n = 5) [19], uncontrolled hypertension (n = 3) [15], [22], proteinuria (n = 2) [19], fatigue (n = 1) [19], delayed wound healing (n = 1) [19], and diarrhea (n = 1) [21]. Detailed reasons for patient withdrawal were not available in all studies.

Discussion

This is the first systematic review to examine the efficacy and safety of bevacizumab for the treatment of advanced HCC. Our review included a total of eight Phase II clinical trials that involved 300 patients. There was a distinct lack of homogeneity among the trials in many respects. However, in general, the results (PFS, OS, tumor response, and toxicities) from these trials indicate that bevacizumab shows promise as an effective and tolerable treatment for advanced HCC.

To date, sorafenib is the only systemic drug therapy approved by the United States Food and Drug administration for the treatment of unresectable HCC. Two Phase III clinical trials have examined the efficacy and safety of sorafenib in patients with advanced HCC. In the SHARP trial [10], median OS in patients treated with sorafenib was 10.7 months, PR was 2%, SD was 71%, and DCR was 43%. In a trial conducted in the Asia-Pacific region [11], median OS in patients treated with sorafenib was 6.5 months, PR was 3.3%, SD was 54.0%, and DCR was 35.3%. Overall, the efficacy of bevacizumab for the treatment of advanced HCC appears to compare favorably with that of sorafenib. Six of the eight bevacizumab Phase II trials reported median OS rates that are similar to or greater than those reported in the SHARP and Asia-Pacific trials [10], [11]. Taken together, these findings are encouraging, and suggest that bevacizumab may prove to be a feasible treatment option for advanced HCC.

Interestingly, none of the patients in the trial reported by Yau et al. [20] responded to treatment. All patients in the trial were refractory to sorafenib and had very advanced HCC. The authors suggested that this lack of a response to sorafenib may have been due to increased proliferation and invasion in the absence of VEGF-related angiogenesis [20]. Given that bevacizumab is also an anti-VEGF therapy, the lack of efficacy is perhaps not completely surprising. This finding suggests that patients who are refractory to sorafenib will receive no benefit from treatment with bevacizumab/erlotinib. It must be noted however, that this trial included a very small number of patients (N = 10). Hence, the results must be interpreted with caution. Further, the findings from Kaseb et al.'s study [18], suggest that patients previously treated with sorafenib (n = 7) may respond to treatment (as indicated by PFS and OS) with bevacizumab given in combination with erlotinib.

There was variability among the studies regarding the dose of bevacizumab given, the co-administered treatment(s), the number of treatment cycles, and the line of treatment. Interestingly, bevacizumab was given in combination with erlotinib, an epidermal growth factor receptor tyrosine (EGFR) kinase inhibitor, in four of the eight studies [18]–[21]. As EGFR is known to promote proliferation of cancer cells [23], dual targeting of VEGF with bevacizumab and EGFR with erlotinib was considered to be a logical treatment approach for advanced HCC. Indeed, the findings from several Phase II studies suggest that erlotinib alone may facilitate disease control [24], [25]. Outcomes were not consistently better or worse with the bevacizumab/erlotinib combination than outcomes associated with the treatment regimens used in other trials. However, the patient populations in the trials involving bevacizumab/erlotinib were far from homogenous, making any meaningful comparison of this treatment combination with other combinations difficult. Clearly, further studies are needed to determine the optimal bevacizumab treatment regimen.

Bevacizumab is known to be associated with a number of toxicities, including nausea/vomiting, diarrhea, fatigue, anorexia, dry skin, hypertension, GI perforation, GI and other bleeding, and thrombosis [26], [27]. There were no unexpected toxicities reported in the Phase II trials of bevacizumab and the vast majority of toxicities were grade 1 or 2 in severity. These findings suggest that bevacizumab was generally well tolerated. Notably, instances of GI bleeding were reported in all but one trial and several patients died due to this complication. The cause of GI bleeding was typically esophageal varices and/or portal hypertension. Patients with these comorbidities (unless controlled in the case of portal hypertension) may not be suitable for treatment with bevacizumab. Indeed, Thomas et al. [19] ultimately implemented a screening process in their trial to identify and exclude patients with esophageal varices before the initiation of treatment. Another notable patient death due to gastric perforation and subsequent sepsis was also associated with esophageal varices (and cirrhosis) [17].

This systematic review has a number of limitations that should be acknowledged. Firstly, none of the trials included were randomized controlled trials. Hence, the evidence from these trials is not of the highest possible quality. Secondly, it is possible that there may be some degree of publication bias in this area of research. We identified several abstracts describing trials that were not further detailed in standard publications; hence, we could not include these trials in the review. Thirdly, there is clearly a multitude of confounding factors (patient and treatment characteristics) that make between trial comparisons difficult. Notably, the severity of concurrent liver disease is likely to have a significant influence on the efficacy of treatment [28]. There were also inconsistencies in intention-to-treat analysis that may have affected outcome data. Finally, few of the studies provided a precise definition of PFS. As previously noted [29], PFS is not infrequently confused with time to progression. Therefore, it is possible that the PFS results extracted from the trials may have actually been a mixture of PFS and time to progression.

In conclusion, the current evidence from Phase II clinical trials suggests that bevacizumab may be a relatively effective and tolerable treatment for advanced HCC. Further, the efficacy of bevacizumab appears to compare favorably with that of sorafenib, the only VEGF inhibitor currently approved for the treatment of HCC. Large scale randomized controlled trials are needed to further investigate this treatment option. In particular, studies are needed to further characterize the efficacy and safety profile, determine which patients are most likely to benefit from treatment, and establish how bevacizumab can be optimally incorporated into HCC treatment strategies.

Supporting Information