Liver resection is recommended as the first line of treatment for patients with early stage HCC with well-preserved liver function [13]. However, resection of even very early tumors, less than 2 cm and without vascular invasion or satellites (BCLC stage 0), is associated with a recurrence rate of approximately 60% at 5 years [13, 14]. HCC patients are often diagnosed at advanced stages when recurrence occurs, and curative therapy options are limited. The prognosis is extremely poor, leading to a 5-year overall survival rate of 2% [3].
The systemic treatment options available for HCC patients with advanced stages are limited. Overall, more than 50% of patients receive systemic therapies at some point during the disease process [15]. Sorafenib, a molecular kinase inhibitor, was thought to be a breakthrough in treating unresectable HCC although only 3 months longer OS was found in SHARP trial [4]. For a decade, sorafenib was the only FDA-approved therapy and the benefits were limited for lack of either therapeutic alternative or second-line treatment for those who are intolerant or resistant. However, since 2017, treatment for patients with advanced HCC is dramatically changed by novel multi-target inhibitors approved, such as regorafenib, lenvatinib and cabozantinib, or immune checkpoint inhibitors, such as nivolumab and pembrolizumab. Regorafenib is an oral multikinase inhibitor that blocks the activity of protein kinases involved in angiogenesis, oncogenesis, metastasis, and tumour immunity [6, 7]. Regorafenib is the only systemic treatment shown to provide survival benefit in advanced HCC patients progressing on sorafenib treatment. RESORCE trial indicated that regorafenib improved OS with a hazard ratio of 0.63 (95% CI: 0.50–0.79; one-sided p < 0.0001); median survival was 10.6 months (95% CI: 9.1–12.1) for regorafenib versus 7.8 months (6.3–8.8) for placebo [6]. Although regorafenib has been approved as a second-line treatment for patients with advanced HCC who show progression after sorafenib therapy, the treatment efficacy remains insufficient. With the development of immune therapy, the treatment effects on HCC need to be urgently explored.
PD-1 is expressed by activated T lymphocytes and is a pivotal immune checkpoint receptor that mediates immunosuppression upon binding to the PD-L1 expressed by tumor cells [9]. In recent years, immune checkpoint blockade has brought a paradigm shift in the treatment of a number of solid tumors. Various immune checkpoint blocking agents are being tested for their efficacy in HCC. Furthermore, PD-1 pathway offers a potential treatment strategy based on the encouraging results of KEYNOTE-224 [16] and Checkmate 040 trials [17]. Reccently, IMbrave150 trial showed better overall and progressionfree survival outcomes of atezolizumab plus bevacizumab as compared with sorafenib in patients with unresectable hepatocellular carcinoma who had not previously received systemic therapy, which inspired us to administrate this combination therapy in advanced or metastatic HCC [12]. Sintilimab (Innovent Biologics, Suzhou, China) is a highly selective, humanised, monoclonal antibody that blocks interactions between PD-1 and its ligands and has been tested regarding the safety and activity in patients with advanced-stage solid tumor and was approved for lymphoma by Chinese Center for Drug Evaluation in China in 2018 [18–20]. Findings from a phase 1 study of sintilimab in advanced solid tumours suggested 200 mg every 3 weeks as the recommended dose, and clinical benefit from the therapy was observed [19, 21].
For those HCC patients with sorafenib resistance, the efficacy of regorafenib combined with PD-1/PD-L1 inhibitors remains unclear. Regorafenib was proved to be an immunomodulator in tumor microenvironment while PD-1 antibody blocks the co-inhibitory signals and unlocks the negative regulation of the immune response [22, 23]. Therefore, further investigations for the combination treatment of regorafenib and PD-1/PD-L1 inhibitors are warranted to provide its efficacy data in clinical trials. Unfortunately, there are no published data from randomized controlled trials in HCC which were registered on clinicaltrial.gov currently (Table 2). Standard combination and sequencing of the therapy need to be established with deeper insight into the rationale of combined action and further RCTs. What’s more, for most of the patients enrolled in, present with preserved liver function, while the advanced HCC patients in real clinical phase may have a much worse performance. Whether they can tolerate the combination treatment is still unknown and the clinical trials won’t take the risk to enroll these patients. Joerger et al. [24] presented the case of a sorafenib-refractory patient probably experiencing progressive disease during immune checkpoint inhibitor combination treatment with the anti-PD-1 monoclonal antibody nivolumab and the anti-GITR monoclonal antibody BMS-986156 within a clinical phase-1 trial followed by a prolonged tumor response according to RECIST v 1.1 during third-line treatment with regorafenib. In this case, sorafenib-immunotherapy-regarofenib sequential treatment was applied and the last evaluation was documented as partial response and the patient started taking regorafenib at a reduced dose of 80 mg and later further reduced to 40 mg per day. The patient in our report was evaluated as complete response after combination therapy of regorafenib with standard dose and sintilimab. No life-threatening adverse events were found in our patient. The combination of regorafenib and PD-1/PD-L1 inhibitor will be a novel therapy method for the future gold standard in the systemic treatment of sorafenib-refractory HCC.
Table 2
Ongoing clinical trials with regorafenib and PD-1/PD-L1 inhibitors in hepatocellular carcinoma.
NCT Number | Study Title | N | Interventions | Trial phase | Primary endpoint | Current status |
NCT 04170556 | Regorafenib Followed by Nivolumab in Patients With Hepatocellular Carcinoma | 60 | Regorafenib + Nivolumab | 1 and 2 | AE TTP | Recruiting |
NCT 04183088 | Regorafenib Plus Tislelizumab as First-line Systemic Therapy for Patients With Advanced Hepatocellular Carcinoma | 125 | Regorafenib+ Tislelizumab | 2 | AE ORR | Not yet recruiting |
NCT 03347292 | Regorafenib Plus Pembrolizumab in First Line Systemic Treatment of HCC | 57 | Regorafenib+ Pembrolizumab | 1 | AE | Recruiting |
NCT 03475953 | A Phase I/II Study of Regorafenib Plus Avelumab in Solid Tumors | 362 | Regorafenib+ Avelumab | 1 and 2 | Phase 1 : Recommended phase 2 Dose Phase 2 : Assessment of the antitumor activity of regorafenib | Recruiting |
NCT 04310709 | Combination of Regorafenib and Nivolumab in Unresectable Hepatocellular Carcinoma | 42 | Regorafenib+ Nivolumab | 2 | RR | Not yet recruiting |
AE, Adverse Events; TTP, Time to progression; ORR, Objective response rate; RR, Response rate. |
The precise mechanism of synergistic effect between regorafenib and PD-1/PD-L1 inhibitors remains unclear. Previous study indicated that inhibition of JAK1/2-STAT1 signaling pathway blocked MHC-I expression while suppressing the MAPK pathway increased MHC-I expression [25]. Through inhibiting both the RET-Src axis/JAK1/2-STAT1 and MAPK pathway, regorafenib had little influence on MHC-I expression. Taken together, through blocking the IFN-γ induced PD-L1 and IDO1 expression with little influence on MHC-I expression, regorafenib unleashed the IFN-γ side effect without compromising the antigen presentation processes. What’s more, tumor-associated macrophage (TAM) is major population of immune cells that affects tumor development. One of the mechanisms described for the failure of anti-angiogenic therapy and tumor evasion is the strong infiltration of TAMs. TAM serves as an important driving factor in immunosuppressive tumor microenvironment (TME) and, for instance, the secreted TGF-β inhibits CD8 + T-cell responses to kill the cancer cells [26, 27]. Regorafenib modulates TAM re-polarization and relieved the immunosuppressive effect of TAM via binding to CSF-1R [27]. Terme et al. [28] demonstrated that regorafenib reduces the proportion of Tregs and inhibits tumor-induced Treg proliferation via targeting the vascular endothelial growth factor A (VEGFA)/VEGF receptor 2 (VEGFR2) signaling pathway. Regorafenib targets a variety of kinases involved in angiogenic, tumor growth-promoting and tumor micro-environmental signalling pathways [7]. The probable mechanism of synergistic effects of regorafenib and PD-1/PD-L1 inhibitors are showed in Fig. 5.
In summary, this study provided the first case of complete tumor response to the combination of regorafenib and sintilimab as second line treatment for a patient with advanced, pulmonary metastatic HCC which was refractory to first-line sorafenib. Data from this clinical case report support future exploration of combination treatment of the oral multi-kinase inhibitor regorafenib with PD-1/PD-L1 inhibitors in sorafenib-refractory HCC patients. Regorafenib plus PD-1 or PD-L1 inhibitor may present a new potential treatment option for the advanced HCC patient with sorafenib resistance. However, their synergistic effects and safety need further investigation in a randomized phase 3 study.