Randomized trials and endpoints in advanced HCC: Role of PFS as a surrogate of survival

Abstract

Hepatocellular carcinoma (HCC) is a major cause of cancer-related mortality worldwide. Around half of patients with HCC will receive systemic therapies during their life span. The pivotal positive sorafenib trial and regulatory approval in 2007 was followed by a decade of negative studies with drugs leading to marginal antitumoral efficacy, toxicity, or trials with a lack of enrichment strategies. This trend has changed over the last 2 years with several compounds, such as lenvatinib (in first-line) and regorafenib, cabozantinib, ramucirumab and nivolumab (in second-line), showing clinical benefit. These successes came at a cost of increasing the complexity of decision-making, and ultimately, impacting the design of future clinical trials. Nowadays, life expectancy with single active agents has surpassed the threshold of 1 year and sequential strategies have provided encouraging outcomes. Overall survival (OS) remains the main endpoint in phase III investigations, but as in other solid tumours, there is a clear need to define surrogate endpoints that both reliably recapitulate survival benefits and can be assessed before additional efficacious drugs are administered. A thorough analysis of 21 phase III trials published in advanced HCC demonstrated a moderate correlation between progression-free survival (PFS) or time to progression (TTP) and OS (R = 0.84 and R = 0.83, respectively). Nonetheless, the significant differences in PFS identified in 7 phase III studies only correlated with differences in OS in 3 cases. In these cases, the hazard ratio (HR) for PFS was ≤0.6. Thus, this threshold is herein proposed as a potential surrogate endpoint of OS in advanced HCC. Conversely, PFS with an HR between 0.6-0.7, despite significance, was not associated with better survival, and thus these magnitudes are considered uncertain surrogates. In the current review, we discuss the reasons for positive or negative phase III trials in advanced HCC, and the strengths and limitations of surrogate endpoints (PFS, TTP and objective response rate [ORR]) to predict survival.

Keywords: FDA approval; Liver cancer; Systemic therapies; Trial design.

Fig. 1.. Median overall survival of treatment modalities assessed in phase III trials for advanced hepatocellular carcinoma.

Treatments with more than one dot represent all the results obtained from different clinical trials testing the same compound. Trials are coloured based on whether the final result was positive for superiority (green), negative (red) or positive for non-inferiority (orange) for the primary endpoint (OS). Placebo appears in blue. Relevant inclusion/exclusion criteria that may impact on median OS are: no portal vein invasion, no pulmonary metastases, sorafenib tolerant, MET high and AFP >400 ng/ml. Star represents pooled individual patient data from REACH and REACH-2 in patients with AFP >400 ng/mL. AFP, alpha-fetoprotein; HAIC, hepatic infusion arterial chemotherapy; OS, overall survival.

Fig. 2.. Treatment strategy for advanced hepatocellular carcinoma.

Adapted from Llovet et al. Nat Rev Clin Oncol 2018. Drugs in green have positive results from phase III trials with a superiority design (sorafenib in the first-line setting and regorafenib, cabozantinib and ramucirumab in the second-line setting). Drugs in orange have positive results from phase III trials with a non-inferiority design (lenvatinib in the first-line setting). Drugs in red have received accelerated approval from the FDA on the basis of promising efficacy results in phase II trials (nivolumab and pembrolizumab in the second-line setting). Key details of the patient populations are provided. AFP, Alpha-fetoprotein; BCLC, Barcelona Clinic Liver Cancer (classification); ECOG PS, Eastern Cooperative Oncology Group performance status; EHS: extrahepatic spread; HCV, hepatitis C virus; HR, hazard ratio; mRECIST, modified Response Evaluation Criteria In Solid Tumors; ORR, objective response rate; OS, overall survival.

Fig. 3.. Correlation between surrogate endpoints and hard endpoint (overall survival).

(A) Correlation between progression-free survival and overall survival. (B) Correlation between time to progression and overall survival. Trial-level correlation between endpoints using criteria from the Institute for Quality and Efficiency in Health Care (IQWIG). R and R2 refers to the weighted Pearson coefficient between the HR of OS and the HR of the surrogate endpoint. IQWIG categorizes the strength of the correlation based on the value of R as low (R <0.7), moderate (R >0.7 to R <0.85) and high (R >0.85). Each dot represents one of the phase III clinical trials conducted on advanced HCC. Size of the dot is proportional to the total number of patients enrolled in the trial. Trials are coloured based on whether the final result was positive, negative or non-inferior for the primary endpoint (OS). X and Y axis depict the value of the HR for the surrogate and the hard endpoint, respectively. Gray shaded areas represent the upper and lower limits of the 95% confidence intervals for the regression. HCC, hepatocellular carcinoma; HR, hazard ratio; OS, overall survival.

Fig. 4.. Correlation between surrogate endpoints (progression-free survival and time to progression).

Trial-level correlation between endpoints. R and R2 refers to the weighted Pearson coefficient between the HR of PFS and the HR of TTP. Each dot represents one of the phase III clinical trials conducted on advanced HCC. Size of the dot is proportional to the total number of patients enrolled in the trial. Trials are coloured based on whether the final result was positive, negative or non-inferior for the primary endpoint (OS). X and Y axis depict the value of the HR for the surrogate TTP and PFS, respectively. Gray shaded areas represent the upper and lower limits of the 95% confidence intervals for the regression. HCC, hepatocellular carcinoma; HR, hazard ratio; OS, overall survival; PFS, progression-free survival; TTP, time to progression.