In this study, we report for the first time the efficacy of SBRT in patients with PD-1 inhibitor–TACE refractory intermediate-stage HCC. The results showed that switching to receive SBRT combined with PD-1 inhibitors provided better long-term prognosis and tumor control than continued receive TACE combined with PD-1 inhibitors. This provides more options for the treatment of patients with BCLC stage B HCC.
TACE is the standard of care for patients with BCLC stage B HCC[6–9], but some patients develop TACE refractoriness and cannot achieve effective tumor control[10, 11]. Guidelines recommend that patients start receiving systemic therapy once they are diagnosed as TACE refractoriness[6, 8, 9]. Currently, the most commonly used drugs for systemic therapy include targeted anti-vascular agents such as sorafenib and lenvatinib. The results of several phase III trials suggest that TACE combined with sorafenib does not improve the long-term prognosis of patients[22–26], whereas the recent Japanese TACTICS trial demonstrated that sorafenib was able to prolong PFS of patients [27], while a large number of retrospective studies proved that the combination therapy of targeted anti-vascular agents and TACE was potentially beneficial for HCC patients[20, 28–32]. Although the efficacy of TACE combined with targeted anti-vascular agents is still controversial, the therapeutic modality of TACE combined with systemic therapy has exhibited its promise[33]. Meanwhile, PD-1 inhibitors have been increasingly investigated as representative agents for immunotherapy. And the possible mechanism of benefit of TACE combined with PD-1 inhibitor was uncovered: TACE could decrease the ratio of CD4+ / CD8+ cells and increase the level of PD-1 mRNA expression in patients with HCC[12]. Therefore, TACE combined with PD-1 inhibitor might have potential clinical value for patients with HCC. This was precisely verified by the recent report by Chen et al., in which patients had increased PD-1 inhibitor treatment on the basis of TACE with improved oncological outcomes[14]. However, the role of PD-1 inhibitors for patients is also limited[34], and once a patient presents refractory to both PD-1 inhibitors and TACE, what treatment should be followed up, which is a question worth exploring and urgently resolving.
Radiotherapy because the stronger hepatotoxicity limits its application, with the advancement of technology, SBRT is currently able to safely deliver high-dose radiotherapy to HCC, and the AASLD guidelines accepted SBRT as one of the treatments for HCC[7]. For patients with BCLC stage B HCC who received SBRT, the 2-year local control rate reached 61-81%[35]. Several retrospective controlled studies containing patients with intermediate stage HCC showed that SBRT had similar or even higher tumor control rates and OS than TACE[18, 19]. On the one hand, a clinical trial demonstrated the safety and feasibility of SBRT as a local salvage regimen for incomplete TACE[36]. Radiotherapy can trigger immunogenic cell death (ICD), resulting in the release of cytokines and damage associated molecular patterns (DAMPs). DAMPs can lead to the subsequent priming and trafficking of tumor specific T lymphocytes into the tumor microenvironment (TME) by enhancing the recruitment of antigen-presenting cells (APCs), the processing of tumor associated antigens (TAAs), and the cross presentation of antigenic peptides on major histocompatibility complex class I (MHC I), thereby enhancing the efficacy of PD-1 inhibitors[37]. And its clinical benefits have also been reported[36, 38, 39]. Therefore, we speculate that SBRT combined with PD-1 inhibitor may be a potential effective alternative treatment for patients who are refractory to PD-1 combined TACE.
Our results validate the above theory and suggest that this therapy of SBRT combined with PD-1 inhibitor can significantly improve the oncological outcomes of patients who are refractory to PD-1 inhibitor combined with TACE. In this study that enrolled 76 patients proven to be refractory to PD-1 inhibitor TACE treatment, the SBRT group (n = 31) had a median PFS of 19.6 months (95% CI 13.1-26.1), which was significantly higher than the TACE group (n = 45) with a median PFS of 10.1 months (95% CI 7.3-12.9, P < 0.001). The 1-year OS rate and 1-year PFS rate in the SBRT group were 71.5% and 64.8%, and the ORR and DCR were 71.0% and 80.6%, respectively. The 1-year OS rate and 1-year PFS rate in the TACE group were 54.2% and 40.7%, and the ORR and DCR were 15.6% and 31.1%, respectively. Compared with TACE, SBRT significantly prolonged PFS (HR = 0.361, 95% CI 0.182-0.716, P < 0.01) and OS (HR = 0.375, 95% CI 0.182-0.773, P < 0.001), with better ORR (OR=8.483, 95%CI 3.319-21.680, P < 0.001) and DCR (OR = 9.226, 95% CI 3.096-27.493, P < 0.001) in PD-1 inhibitor–TACE refractory patients. In addition to efficacy, we analyzed TRAEs associated with SBRT plus PD-1 inhibitors. The most common TRAEs were increased AST (51.6%), fatigue (48.4%), and decreased platelet count (48.4%). The most common grade 3/4 TRAEs were lymphopenia (9.7%) and dysphagia (6.5%). This is close to previous reports[40], with no unexpected TRAEs present. Therefore, SBRT combined with PD-1 is an effective and safe treatment modality for patients with PD-1 inhibitor–TACE refractory intermediate-stage HCC.
This study has several limitations. First, this is a retrospective study with inherent defects. Second, the sample size included in this study was small with potential selection bias. Third, there was some heterogeneity in patient populations and treatment regimens, which may have affected our findings. A prospective study is therefore needed to confirm our conclusions.
In conclusion, switching to receive SBRT was effective as evidenced by an increase in PFS and OS in patients with PD-1 inhibitor–TACE refractory intermediate-stage HCC. To improve the survival of those patients, it is important to switch treatment from TACE to SBRT even if the tumor is still in the intermediate stage.