AIM: To demonstrate that administering heparanase inhibitor PI-88 at 160 mg/d is safe and promising in reducing hepatocellular carcinoma (HCC) recurrence for up to 3 year following curative resection.

METHODS: A total of 143 patients (83.1% of the 172 participants in the phase II study) participated in the follow-up study. Of these patients, 50 had received no treatment, 48 had received 160 mg/d PI-88, and 45 had received 250 mg/d PI-88 during the phase II trial. Safety parameters and the following efficacy endpoints were investigated: (1) time to recurrence; (2) disease-free survival; and (3) overall survival.

RESULTS: PI-88 at 160 mg/d delayed the onset and frequency of HCC recurrence, and provided a clinically significant survival advantage for up to 3 years after treatment compared with those of the control group: (1) the recurrence-free rate increased from 50% to 63%, and (2) time to recurrence at the 36th percentile was postponed by 78%. The efficacy of administering PI-88 at 250 mg/d was confounded by a high dropout rate (11 out of 54 patients). Additionally, subgroup analyses of patients with (1) multiple tumors or a single tumor ≥ 2 cm; and (2) hepatitis B or C revealed that administering PI-88 at 160 mg/d conferred the most significant survival advantage (56.8% improvement in disease-free survival, P = 0.045) for patients with both risk factors for recurrence.

CONCLUSION: Administering PI-88 at 160 mg/d is a safe and well-tolerated dosage that may confer significant clinical benefits for patients with HCC.

Hepatocellular carcinoma (HCC) is currently the fifth most common cancer and the third leading cause of cancer related deaths worldwide[1]. Traditionally, HCC has been more prevalent in Asia because of the prevalence of hepatitis B virus (HBV) infection. However, the incidence of HCC in the United States and Europe has risen in recent years because of increases in the number of hepatitis C virus (HCV) infections, consequently generating more interest in HCC research and treatment worldwide[2].

Surgical resection is a potentially curative therapy used to treat early-stage HCC; however, 50% to 80% of resection patients experience recurrence within 5 years[3,4]. Although numerous treatments, including oral and regional chemotherapy, interferon α and β, preoperative chemoembolization, and adoptive immunotherapy, have been investigated to reduce HCC recurrence, inconsistent and inconclusive results have prevented the adoption of these treatments in clinical practice[5-7]. Hence, there remains a dire clinical need for an adjuvant therapy to reduce the risk of postresection HCC recurrence[4,7,8].

There are 2 main types of postresection HCC recurrence. Intrahepatic metastatic recurrences develop from undetectable HCC dissemination prior to resection. De novo recurrences develop multicentrically and metachronously in the background liver, usually in patients with cirrhosis or chronic hepatitis[4,8]. Intrahepatic metastatic recurrence typically occurs within 2 years following resection, and de novo recurrence typically occurs 2 years following resection[6]. Although researchers who have conducted relevant molecular studies can differentiate between these types of recurrences to determine appropriate treatment strategies, these strategies are not widely used in clinical settings[4,8]. Currently, for convenience, recurrence in clinical settings is categorized as early or late, occurring within or after 2 years postresection, to approximate the likely mode of recurrence. Ideally, adjuvant therapies used to decrease postresection recurrence can inhibit both types of recurrence[4].

PI-88, a heparanase inhibitor, reduces HCC recurrence through 3 mechanisms. By inhibiting heparin sulfate (HS) degradation, PI-88 (1) preserves the integrity of the extracellular matrix (ECM) and (2) suppresses the release of angiogenic and fibroblastic growth factors (GFs) from the ECM. Moreover, the strong affinity of PI-88 to GFs enables PI-88 to (3) aggregate released GFs and block their activity. The antiangiogenic property of PI-88 stems from its ability to antagonize GF reception, and thereby restrict the necessary blood supply for both intrahepatic metastatic and de novo tumor proliferation. The antimetastatic property of PI-88 may stem from its ability to preserve ECM integrity, and thereby decrease basement invasion to further suppress intrahepatic metastatic recurrences[9-12]. Considering its ability to perform these dual functions, PI-88 can potentially suppress both types of HCC recurrences.

To investigate PI-88 as an adjuvant therapy for HCC recurrence, a randomized, multicenter Simon’s 2-stage design phase II trial was previously conducted to determine its safety, optimal dosage, and preliminary efficacy. The study results indicated that administering 160 mg/d for 36 wk postresection was a safe and optimal dosage that increased recurrence-free survival at 48 wk[13]. This observational follow-up study to the phase II trial was conducted to determine whether these effects lasted longer than 48 wk and improved overall survival.

In the previous phase II study, the primary endpoint was the recurrence-free survival rate; in this follow-up study, its more conventional equivalent, disease-free survival (DFS), was assessed. The efficacy endpoints analyzed in this follow-up study included (1) time-to-recurrence (TTR); (2) DFS; and (3) overall survival (OS). DFS and OS were assessed because both are reliable, clinically relevant endpoints[8]. This follow-up study also included subgroup analyses and further investigation to prepare for the design of a double-blind, randomized phase III confirmatory study.

The results of this follow-up study corroborated the findings of the phase II study: PI-88 administered at 160 mg/d is well-tolerated and may be effective in reducing HCC recurrence. Furthermore, previously observed clinical benefits during the initial 36 wk of active treatment persisted for up to 3 years with minimal AEs. Because numerous premature withdrawals caused by treatment-related toxicities occurred, PI-88 administered at 250 mg/d (Group C) did not confer significant clinical benefits. The following discussion focuses on the 160 mg/d dosage.

Overall, these results suggest that PI-88 administered at 160 mg/d may confer clinical benefits on HCC patients whose tumors have been surgically removed with curative intent. The 36-wk 160 mg/d PI-88 treatment delayed median TTR to over 3 years, and decreased the 3-year TTR probability by 21.8%. In addition to delaying the onset and decreasing the frequency of recurrence, PI-88 treatment also conferred survival advantages; the DFS rate of the 160 mg/d cohort, 49.4%, was the highest rate observed among the cohorts and demonstrated a 28.1% improvement compared with that of the control group. Similar DFS improvements observed at the end of the phase II and follow-up studies (26.4% and 28.1%) suggest that the survival benefits of short term PI-88 treatment were maintained for 2 additional years without implementing additional treatment. The OS results, as expected in a small population study for adjuvant cancer therapy, were inconclusive. Although the clinical benefits did not reach statistical significance, active treatment was limited to only 36 wk in the original phase II study, and the prolonged use of 160 mg/d PI-88 may result in more pronounced benefits; further trials are necessary to verify this.

Patient stratification observed using subgroup analyses further supported PI-88 efficacy. Because the presence of multiple tumors or a single tumor ≥ 2 cm was correlated with high degrees of intrahepatic tumor spread and vascular invasion[5], patients with multiple tumors or a single tumor ≥ 2 cm, together with chronic HBV and HCV infection, are more susceptible to recurrence after surgery. The decreasing DFS probabilities in the untreated cohort exemplify this trend (Table 4). Moreover, the constant DFS probabilities and increasing DFS improvements in the treated intermediate-risk and high-risk groups reinforce the efficacy of PI-88 in reducing recurrence, and also suggest that its effects may be more pronounced in patients with factors that promote HCC recurrence.

The high-risk subgroup exhibited a DFS improvement of 56.8% at the end of the phase II study (P = 0.045), and this result was statistically significant. Although this rate of DFS improvement was maintained up to the end of this follow-up study, the magnitude of this improvement was not statistically significant (P = 0.163). This suggests that the change in DFS improvement is not a reflection of PI-88 treatment efficacy; instead, it is possibly a reflection of the decrease in sample size, which may have prevented clinically significant benefits from reaching statistical significance. Thus, a larger patient population is required in the phase III study to verify the statistical significance of the clinical efficacy of PI-88.

As per expert suggestion[8,15], the TTR and OS endpoints were also assessed in this follow-up study. The TTR endpoint effectively revealed the efficacy of PI-88 in delaying recurrence. Although certain regulatory agencies prefer using OS as a measure of efficacy, properly powering OS as an early-stage cancer adjuvant therapy may be difficult for multiple reasons. One reason is that other therapeutic modalities, such as alternative medicine, may confound the efficacy and survival advantages of the treatment under study. Another reason is that, because resection is potentially curative, the extended observation time may have allowed deaths unrelated to the treatment or HCC recurrence to confound the study data. Finally, compliance to PI-88 and access to other therapy or medicine for the treatment of recurrent HCC may also confound the OS. In this observation study, treatment strategy for the recurrent tumor was determined individually by the investigator. Selection bias may significantly influence the overall outcomes of HCC recurrence, which however could not be controlled. Thus, the inconsistent OS probabilities observed in this study may be attributed to these reasons or to the limited sample size.

To investigate the implications of patient heterogeneity, as suggested by Forner and Roayaie[15], subgroup analysis excluding the 4 (2 patients each from Groups A and B) borderline Child-Pugh B patients was performed. Unfortunately, because of the small sample size, the results were inconclusive (Figure 3).

The results of this study were consistent with the known mechanisms of PI-88. As a heparanase inhibitor, PI-88 (1) antagonizes interactions between angiogenic GFs and their receptors; (2) inhibits the release of HS-bound angiogenic and fibroblastic GFs; and (3) inhibits the heparanase degradation of ECM[9]. Collectively, these mechanisms produce the antiangiogenic and antimetastatic effects of PI-88, enabling it to simultaneously reduce intrahepatic metastatic and de novo HCC recurrences. However, because the causes of de novo recurrences are multifactorial, administering combinational therapy using agents with various mechanisms, such as antiviral or other molecular target agents, may confer even greater clinical benefits[16-18].

In addition to limitations in sample size, additional factors may have precluded the attainment of more statistically significant outcomes in this study. Because active cancer treatments are typically administered until either progression or recurrence occurs, prolonged active PI-88 treatment may have conferred even more favorable survival benefits than those observed. Moreover, because resection is potentially curative, extrapolating the length of time required to achieve statistically significant outcomes is difficult, especially because resection and death rates are declining because of technological advances[19,20].

Overall, the findings of this follow-up study are consistent with the findings of the original study, and provide insights that can be used to aid the design of a more conclusive phase III trial for the approval of adjuvant PI-88. High tumor recurrence rates and the lack of a standard of care following resection have created a dire need for adjuvant HCC agents; based on the results of the current study, PI-88 is a promising candidate for fulfilling that need.

We extend our thanks to the researchers who participated in this PI-88 HCC phase II study: Lin YJ, Shan YS, and Chou TC of National Cheng Kung University Hospital, Tainan, Taiwan; and Tsai CC and Wang BW of Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan. We are indebted to James Wang and Angela Tseng for their statistical assistance. We would also like to thank our study coordinators Chen CY, Lee R, and Lai R for their contributions to this follow-up trial.