This is the first clinical trial of a systemic anti-angiogenic agent used in combination with TACE. At the time that this investigator-initiated pilot trial was initiated in 2003, systemic anti-angiogenic agents were unproven in HCC. Subsequent to the initiation of this study, a molecularly-targeted approach for the treatment of advanced HCC was validated by the SHARP trial, which demonstrated an improvement in overall survival with sorafenib compared to placebo . However, the use of molecularly-targeted agents in advanced disease may not take full advantage of the potential activity of this class of agents. Anti-angiogenic agents are now being tested in large multi-institutional phase III trials for subjects with early stage HCC, as an adjunct to TACE, RFA, and resection. The results of this pilot study of TACE plus or minus bevacizumab demonstrate that anti-angiogenic agents are a tolerable adjunct to TACE, and set the stage for larger clinical trials examining this approach.
TACE in HCC provides a unique opportunity to study neovascularity in real time, because angiograms are performed as part of the therapeutic procedure. In this study, angiograms were used qualitatively to determine neovascularity on a 0 to 3+ scale at 10 and 14 weeks after TACE, and with this technique, there was a trend towards decreased neovessel formation in subjects who received bevacizumab compared to those who did not. In contrast, bevacizumab did not protect against recanalization, perhaps because recanalization represents a mechanical failure of the embolization material rather than a response to tumor hypoxia. In addition to the qualitative analysis of neovessel formation, tumor blood supply was quantified by measuring blood vessel density in a representative field on the angiogram, much like microvessel density is assessed by immunohistochemisty in tumor biopsies. There was no significant difference in the angiographic blood vessel density between the two treatment arms. The failure to demonstrate a decrease in blood vessel density in the combination arm may be explained by either a true lack of benefit or by a limitation of the methodology employed. Other studies of anti-angiogenic agents in advanced HCC have examined vessel permeability, and tumor blood volume and blood flow using dynamic contrast enhanced MRI (DCE-MRI) or perfusion CT [22, 23]. In recent years, there has been an increasing interest in the use of these techniques as surrogates of microvessel density as measured by immunohistochemistry , and there is an ongoing effort to incorporate in vivo assessments of tumor angiogenesis into clinical trials of anti-angiogenic agents.
The statistically significant improvement in PFS observed in the TACE-BEV arm is interpreted with caution, due to the small sample size. Progression was taken as any new sign of tumor activity, including neovascularity on angiogram, new enhancement of an existing lesion by CT or MRI, or development of a new lesion, according to institutional practice. There was a low threshold for determining progressive disease, because TACE was often used as a bridge to transplant, and earlier treatment could potentially prevent subjects from becoming ineligible for transplant due to tumor volume. The modified Response Evaluation Criteria in Solid Tumors (mRECIST) criteria for hepatocellular cancer, in which disease assessments are based on the sum of the diameters of viable disease rather than on the sum of the total diameters of the target lesions, were published after this study had begun . The mRECIST criteria were not applied retrospectively because the majority of subjects on this trial were imaged with CT rather than MRI, and ethiodol used during TACE obscured the CT findings of enhancement.
There was no statistically significant difference in overall survival between the two treatment arms, with a median survival of 49 months for the TACE-BEV arm, and 61 months for the TACE-O arm. Beyond 36 months, the ability to estimate the survival curves with any precision is impaired due to small sample size and wide confidence intervals. Analysis of overall survival is further hampered by the cross-over design. Any perceived difference in overall survival cannot be attributed to bevacizumab toxicity, because there were no bevacizumab-related deaths, and all subjects succumbed to underlying disease. As a whole, the striking overall survival rates in this pilot study are undoubtedly due to the fact that 12 of the 30 subjects enrolled were ultimately transplanted.
At the initiation of this trial, there was no prior experience with bevacizumab in HCC, and there were concerns regarding the safety of bevacizumab in subjects with an increased risk of bleeding. Several layers of protection were built into the study to address this issue, including a minimum platelet count of 60 to 100,000/μL (depending on the time of enrolment), mandatory endoscopy for any subject with a prior history of grade III varices or gastrointestinal bleeding, and careful follow-up. During the core phase, none of the 15 TACE-BEV subjects developed gastrointestinal bleeding, while one TACE-O subject experienced grade 3 variceal bleeding. During the continuation phase, 3 of the 13 (9 TACE-BEV and 4 cross-over) subjects who received bevacizumab developed grade 2/3 treatment-related gastrointestinal bleeding, but no episode was life-threatening. In addition, while every effort was made to prevent subjects from receiving bevacizumab at the time of OLT, one subject was transplanted 9 days after his last dose of bevacizumab, fortunately without incident. This experience is difficult to directly compare with the contemporaneous phase II trial of single-agent bevacizumab in advanced HCC that reported an 11% incidence of serious bleeding, including one fatal event, because the advanced HCC study included a higher proportion of Child's class B subjects . As the field moves forward with the evaluation of anti-angiogenic agents in early stage HCC, caution regarding the risk of bleeding and the potential for decreased wound healing in this special population is advised.
The PK parameters for bevacizumab observed in the small number of subjects (n = 15) were within the range expected for oncology subjects in general. The population PK model of bevacizumab was based on a heterogeneous population that included subjects with liver metastasis, yet liver function enzymes (e.g., alkaline phosphatase and serum glutamic oxaloacetic transaminase) were not covariates that significantly influenced bevacizumab PK. These clinical findings are substantiated by a preclinical study in rats in which hepatic dysfunction induced by bile duct ligation did not alter the exposure (AUC0 - 11) of bevacizumab following a single 20 mg/kg IV bolus injection . Overall, based on these findings, well-compensated subjects with hepatocellular carcinoma are expected to have predictable bevacizumab disposition.
Serum VEGF levels increased after TACE in both study arms, as described in previous studies [10, 12, 17], but the administration of bevacizumab appeared to mitigate this effect. These results demonstrate that post-TACE VEGF levels can be modulated by bevacizumab, thereby reducing the ability of TACE to stimulate VEGF-mediated angiogenesis.
In summary, this study demonstrates that TACE combined with bevacizumab is safe and feasible in carefully-selected subjects with HCC. The size of the study limits any strong conclusions regarding efficacy, and ultimately a large randomized study would be required to determine if there is an improvement in outcome with the addition of bevaczicumab over TACE alone. Since this study was first designed and implemented, there have been many advances in the field, including confirmation of proof of principal for anti-angiogenic agents in advanced HCC , incorporation of novel imaging modalities to monitor angiogenesis in vivo , adaptation of standardized response criteria in HCC , and the development of doxorubicin-impregnated beads for TACE . Larger ongoing studies with agents such as sorafenib and brivanib will help clarify the role of systemic anti-angiogenic agents as an adjunct to TACE. This pilot study, though limited by the state of the art at its inception, provides further support for this approach.