Background
While the incidence of hepatocellular carcinoma (HCC) is rising worldwide [
1], only 25% of patients benefit from curative treatment and transarterial chemoembolisation (TACE) appears the only palliative therapy with proven benefit for intermediate stages of the tumor [
2‐
4]. For patients with advanced or metastatic disease, no standard treatment has been established resulting in a life expectancy of less than 10% at 3 years. Systemic chemotherapy in particular has been disappointing, not only because of the chemoresistance of HCC, but because of major side-effects poorly tolerated by patients with liver cirrhosis.
Immunomodulation is a promising experimental strategy against HCC [
5]. While interferon-based therapy has also been poorly tolerated with little benefit in clinical trials, thymostimulin showed an overall response rate of 24% associated with a significant increase in life expectancy in the only clinical phase II trial to date [
6]. Moreover, virtually no side-effects were apparent. Isolated from calf thymus, thymostimulin is a standardized low-molecular protein fraction including thymosin-α1 and thymic humoral factor [
7,
8]. It has been shown to induce the proliferation and differentiation of T-lymphocytes and to stimulate the release of interferons and interleukin-2 [
9].
In vitro, thymostimulin activates a selective dose-dependent cytotoxic reaction of Kupffer cells against HCC cell lines [
10]. However, the antineoplastic effect
in vivo and thus the patients likely profiting from therapy remain unclear.
This phase II trial was designed to substantiate the safety and efficacy of thymostimulin in the treatment of advanced HCC and identify clinical criteria to select patients benefiting from a randomized, controlled trial.
Methods
Eligibility
Patients with locally advanced or metastatic HCC not amenable to or failing established treatment were enrolled. Lesions were histologically proven or highly suspicious of HCC in two independent imaging techniques with elevated α-fetoprotein levels (AFP) over 400 ng/ml. Pretreatment of the HCC was allowed in case of tumor progress with the respective therapy; however, no treatment was to be given for at least 3 weeks prior to enrollment. Patients were required to be between 18 and 80 years of age and have an ECOG performance status of ≤ 3. Exclusion criteria were pregnancy/lactation, active second malignancy, severe concomitant disease (e.g. NYHA III-IV, serum creatinine level > 300 μmol/l) or severe decompensated liver function (bilirubin > 5 mg/dl, INR ≥ 2.3). None of the patients received anti-viral treatment with interferon. Ethical approval was obtained from the local ethical review board before study initiation and written informed consent from each patient before entering the study. The study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki and the guidelines on good clinical practice.
Study design
The study was designed as a prospective, uncontrolled and single-centre phase II trial, investigating effect and safety of thymostimulin in patients with advanced HCC. In case of tumor regress, secondary treatment of the HCC with loco-regional modalities was permitted. Primary endpoints of the study were overall survival as well as 1-, 2- and 3-year survival, secondary endpoints tumor response and progression-free survival according to standard WHO criteria, as well as toxicity according to ECOG criteria [
11,
12].
Treatment
Thymostimulin is a licensed immunomodulating drug prepared from an extract of peptides from bovine thymus glands (Thymophysin CytoChemia® 25/50). Following removal of high-molecular cell components and proteins, the low-molecular active thymus peptides are isolated and standardized to a defined protein fraction. All patients received thymostimulin 75 mg subcutaneously for 5 days a week according to manufacturers specifications in addition to best supportive care as required. Treatment with thymostimulin was continued until one of the following criteria was met: disease progression, death of patient, unacceptable toxicity, patient refusal or incompliance, complete response for more than 5 months. Patients with tumor regress were allowed non-systemic concomitant treatment with radiofrequency thermal ablation (RFTA) or transarterial chemoembolisation (TACE), if the tumor was found to be accessible secondary to the study treatment. In case of tumor progress, patients were allowed to receive salvage therapy at the investigator's discretion.
Pretreatment and follow-up evaluation
Pre-treatment and follow-up evaluation included a complete medical history, physical examination, blood count and chemistry as well as performance status. Cause, risk factors and extent of liver disease according to Child-Pugh status as well as prior treatment modalities were recorded at baseline. Tumors were assessed by abdominal ultrasound, chest X-ray and either dynamic computerized tomography (CT) or magnetic resonance imaging (MRI); Okuda- and CLIP-classifications were used for staging. Follow-up investigations were conducted at 6 and 12 weeks, and every three months thereafter until the end of the study. They also included survival data and documentation of concomitant therapies and toxicity of the medication. Tumor response was measured using abdominal ultrasound and CT or MRI scanning and evaluated according to WHO criteria by an experienced radiologist (C. Behrmann).
Statistical methods
All analyses were by intention to treat. Comparisons of continuous variables were done by the Wilcoxon rank-sum method and for categorical variables by the Fisher's exact test. Survival time and progression-free survival were calculated from the start of therapy to the date of death or date of progression/death without progression, respectively. Surviving patients with a complete response were censored at the time of analysis. Survival curves were established with the Kaplan-Meier method, a stepwise forward Cox's regression analysis of survival was used to assess baseline predictors and the treatment effect simultaneously. The following variables were chosen for the univariate analysis: age, sex, weight, the presence of liver cirrhosis and Child classification, Okuda stage and CLIP score, AFP-level, multifocal tumor manifestation, ascites, vascular invasion, extrahepatic metastases, treatment with thymostimulin and treatment with other therapy modalities before or after study entry. Significant variables in the univariate analysis were introduced into the multivariate analysis. Calculations were done with the SPSS package (version 12.0.1).
Discussion
While TACE has become the palliative treatment of choice for HCC in patients with preserved liver function and tumors limited to the liver parenchyma [
13,
14], there is no standard treatment for HCC exceeding these criteria or failing conventional therapy. In our phase II study, we used the immunomodulatory compound thymostimulin, a standardized thymic peptide fraction, to treat patients with advanced HCC not suitable or refractory to therapy options such as resection, RFTA or TACE. A similar phase II study was published in 1996 on 46 patients with advanced HCC not eligible for surgery, reporting an overall tumor response rate of 24% and a tumor control rate of 63% [
6]. 13% of patients obtained a complete response with a median duration of 19 months and a median survival of 27 months compared with 4 months in the 37% of patients with progressive disease. Despite the promising results however, the publication missed out criteria to distinguish between responders and non-responders to thymostimulin and thus to select patients who would likely benefit from treatment.
Similar results were obtained in our study using thymostimulin with a one- and two-year-survival better than anticipated by Okuda [
15] or the Clip Study Group [
16], bearing in mind the selection of our patients not suitable or refractory to conventional therapy (Table
5). Recently, the Barcelona Clinic Liver Cancer (BCLC) staging classification was established proposing treatment options and survival probabilities for early (A), intermediate (B), advanced (C) and terminal (D) stage HCC [
17]. Data for stage C and D of the disease were in part based on an analysis of the combined control arms of a chemoembolisation and a tamoxifen trial, thus providing the natural history of untreated HCC [
18]. While patients in group C still had a 1-, 2- and 3-year survival of 29%, 16% and 8%, respectively, patients in group D had a life expectancy of less than 6 months. Comparisons with our data are complicated by the fact that our study population included patients with both, BCLC stage C and D of the disease. However, an effect of thymostimulin over best supportive care will only be proven in a randomized controlled trial, highlighted recently by the failure of other alternative treatment options such as doxorubicin, tamoxifen or octreotide in meta-analyses or phase III studies [
19‐
21]. The only possible new therapy for advanced HCC with a survival benefit over best supportive care in a large controlled trial is the protein kinase inhibitor sorafenib, presented to date only in a meeting abstract [
4,
22]. Its effect, however, has only been proven for selected patients with well-preserved liver function (not more than 5–6 Child Pugh points) and at the expense of common side-effects in up to 78% of cases [
23,
24].
Table 5
Patient survival overall and by Okuda stage and CLIP score
Overall | 50 % | 23 % | 26 % | 15 % | 48 % | 28 % |
Okuda stage | | | | | | |
I | 69 % | 38 % | 49 % | 32 % | 68 % | 48 % |
II | 40 % | 11 % | 18 % | 9 % | 36 % | 13 % |
III | 0 %* | 0 %* | 3 % | 3 % | 21 % | 10 % |
CLIP score | | | | | | |
0 | 100 %* | 100 %* | | | 84 % | 65 % |
1 | 70 % | 40 % | | | 66 % | 45 % |
2 | 60 % | 20 % | | | 45 % | 17 % |
3 | 30 % | 10 % | | | 36 % | 12 % |
4–6 | 14 %* | 0 %* | | | 9 % | 0 % |
Interestingly, the Barcelona data showed cancer-related symptoms and an invasive HCC phenotype with vascular invasion or extrahepatic spread to be the best predictors of outcome for intermediate and advanced tumors [
18]. In contrast, outcome in our study rather depended on liver function and intrahepatic tumor growth (presence of liver cirrhosis and Okuda stage) in addition to response to thymostimulin, while an invasive or metastatic HCC phenotype had no influence in the multivariate analysis. It may thus be speculated, that the immunmodulatory effect of thymostimulin requires a functioning immune system. All postulated antineoplastic pathways of thymostimulin – stimulation of T lymphocytes to release interleukin-2 and interferons or activation of Kupffer and Natural Killer cells with release of tumor necrosis factor-α [
9,
10] – are impeded by a deteriorating liver function [
25‐
27]. Indeed, HCC growth itself has been linked to a depressed immune function in patients with liver cirrhosis [
28]. Thus, the therapeutic impact of thymostimulin appears also to depend on a preserved liver function and a limited intrahepatic tumor size.
An effect of the treatment modalities prior or in addition to thymostimulin has to be assumed in our study. Even though the response to thymostimulin only, not treatment with other modalities, was selected as a prognostic factor in the multivariate analysis of overall survival, progression of the tumor was dependent on a multimodal treatment. Obviously, thymostimulin is solely a palliative treatment of HCC, although with a reasonable tumor response rate (18%) and very good tumor growth control (79%) in the present series compared with conventional chemotherapy [
14]. Since virtually no side-effects were evident in this and the previous phase II study [
6], it might well be a suitable immunomodulatory component of a multimodal antineoplastic therapy [
29‐
31].
Conclusion
In conclusion, this phase II study confirms the previous report on the potential efficacy and excellent safety profile of thymostimulin in the treatment of HCC. As palliative treatment, a controlled trial is required to unequivocally demonstrate the superiority of thymostimulin over best supportive care. Selection of the target population appears to be necessary regarding liver function and intrahepatic tumor growth, while an invasive or metastatic HCC phenotype has no impact on tumor response. Thus, thymostimulin might be a suitable and well-tolerated component of a multimodal therapy concept for advanced HCC, in particular in combination with local ablative strategies.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
MMD analyzed the data, drafted and finalized the manuscript, and coordinated its submission. CMB and LJ enrolled patients in the clinical protocol. SB performed the statistical analysis. CB evaluated the CT and MRI scans. WEF conceived the study and was the primary investigator. All authors read and approved the final manuscript.