4. Discussion
In the present study, the efficacy of lenvatinib as second-line therapy after atezolizumab plus bevacizumab for patients with unresectable HCC was examined. The American Society of Clinical Oncology (ASCO) guidelines state that second-line treatment with TKIs such as sorafenib, lenvatinib, cabozantinib, and regorafenib may be feasible after first-line atezolizumab plus bevacizumab therapy, but the level of evidence for such treatment is low [
9]. The ASCO guidelines state that the choice of second-line therapy should be based on patient and clinician preference, comorbidities, general condition, and benefit of therapy. The European Society for Medical Oncology clinical practice guideline recommends sorafenib, lenvatinib, regorafenib, cabozantinib, and ramucirumab all side by side as second-line therapy after atezolizumab plus bevacizumab combination therapy [
10]. The American Association for the Study of Liver Diseases has a flowchart showing atezolizumab plus bevacizumab as first-line therapy, sorafenib and lenvatinib as second-line therapy, and regorafenib, cabozantinib, and ramucirumab as third-line therapy [
11]. Clinical practice guidelines for hepatocellular carcinoma of The Japan Society of Hepatology (4th JSH-HCC guidelines) listed atezolizumab plus bevacizumab as first-line, sorafenib and lenvatinib as second-line, and regorafenib, cabozantinib, and ramucirumab as third-line. In addition, in the 2021 edition of the JSH-HCC guidelines, the combination of atezolizumab plus bevacizumab was selected as the first-line therapy, and sorafenib, lenvatinib, regorafenib, cabozantinib, and ramucirumab were all treated in parallel as second-line therapies. All guidelines have in common the recommendation of sorafenib or lenvatinib as first-line therapy and regorafenib, cabozantinib, or ramucirumab as second-line or later therapy when the combination of atezolizumab plus bevacizumab is difficult to use due to autoimmune disease or other reasons.
Recently, network analyses of OS and PFS have been reported for various molecular-targeted agents (MTAs) and immune checkpoint inhibitors (ICIs) for unresectable HCC, by first-line and second-line treatment [
12,
13]. However, there have been no randomized, controlled trials in patients after atezolizumab plus bevacizumab, and given that the REFLECT trial comparing sorafenib and lenvatinib was a non-inferiority trial, it is considered that sorafenib, lenvatinib, regorafenib, cabozantinib, and ramucirumab in patients with AFP >400 ng/ml are all candidate second-line therapies.
Although there is no established evidence for second-line therapy after first-line atezolizumab plus bevacizumab combination therapy for unresectable HCC, the present study showed the efficacy and safety of subsequent systemic therapy in patients who progressed on first-line atezolizumab-bevacizumab. In the present study, the response rate to lenvatinib was 33.3% by RECIST and 54.2% by mRECIST in the 24 patients. Although PFS was 4.0 months, OS after atezolizumab plus bevacizumab was 15.3 months. In the REFLECT trial, the ORR of lenvatinib by mRECIST was 40.6%, and the median OS was 13.6 months, so the present results showed better outcomes. On multivariate analysis, the patients with good liver function before lenvatinib after atezolizumab plus bevacizumab and those with low intrahepatic tumor volume showed significant differences, contributing to the good therapeutic effect of lenvatinib after atezolizumab plus bevacizumab. Therefore, it is important to be careful not to decrease liver function with atezolizumab plus bevacizumab. In addition, the therapeutic effect of lenvatinib after atezolizumab plus bevacizumab was found to be good when the tumor occupied a small percentage of the liver. Regarding AEs, hypertension, fatigue, anorexia, diarrhea, proteinuria, and hand-foot syndrome were seen in the present study, and they were similar to the side effects seen in the REFLECT study. Therefore, it was found that the AEs of lenvatinib after atezolizumab plus bevacizumab were comparable to those of lenvatinib alone.
One of the reasons why the combination of TKIs such as lenvatinib and ICIs such as atezolizumab plus bevacizumab are effective for HCC is due to VEGF inhibition. HCC is a hypervascular tumor and is known to express high levels of VEGF [
14]. In addition, VEGF is known to be associated with immunosuppression in the tumor microenvironment during the cancer immune cycle, creating an environment in which CD8-positive (CD8+) T cells are ineffective [
15,
16]. Specifically, VEGF suppresses dendritic cell maturation and T cell activation in lymph nodes, inhibits CD8+ T cell infiltration into tumors, and differentiates and induces immunosuppressive cells such as regulatory T cells (Tregs). VEGF inhibition may release these factors, thereby creating an environment in which CD8+ T cells can exert their effects.
Abundant infiltration of CD8+ T cells in tumor tissue is considered important for ICIs to have a good therapeutic effect. It has also been reported that ICIs are less effective when there are many Tregs present that suppress the function of effector T cells such as CD8+ T cells, etc. To increase the efficacy of ICIs, it is important to balance the tumor microenvironment with a predominance of CD8+ cells over Tregs by inhibiting VEGF, as bevacizumab does. Similar to bevacizumab, lenvatinib is a multikinase inhibitor that targets not only VEGF receptors 1–3, but also fibroblast growth factor receptors 1–4, platelet-derived growth factor receptor alpha, rearranged during transfection, and KIT [17-20]. Therefore, the therapeutic effect of atezolizumab is expected to be enhanced by the VEGF inhibitory effect of lenvatinib.
It has been reported that a method to monitor the binding of anti-PD-1 antibodies to CD8+ T cells was found, and anti-PD-1 antibodies remains bound to CD8+ T cells for more than 20 weeks after patients stop treatments [
21]. Therefore, it is assumed that the therapeutic effect of lenvatinib was added to the prolonged effect of the ICIs, and that it exerted its effect on immune cells and tumor cells.
Another reason why lenvatinib showed therapeutic efficacy after atezolizumab plus bevacizumab is that lenvatinib worked for ICI-refractory HCC. Factors that contribute to ICI refractoriness include Wnt/β-catenin signaling. It has been reported that HCC patients treated with ICIs was associated with lower DCR, shorter median PFS, and shorter median OS if they had altered activation of Wnt/β-catenin signaling [
22]. On the other hand, it has been reported that Wnt/β-catenin mutations correlated with high expression of FGFR4, and lenvatinib was shown to be highly effective against HCC with high expression of FGFR4 with the ORR of 81% and PFS of 5.5 months, compared to the ORR of 31% and PFS of 2.5 months with low expression of FGFR4 [
23,
24]. There was a case report that described a patient with HCC with a β-catenin mutation, in whom lenvatinib after atezolizumab plus bevacizumab allowed the patient to progress to conversion surgery [
25]. In addition, a case was reported in which a response to atezolizumab plus bevacizumab was achieved in the main intrahepatic tumor, but adrenal metastasis showed disease progression, and subsequent administration of lenvatinib resulted in shrinkage of the adrenal metastasis and conversion to surgery [
26]. There have been reports of differences in responses to ICIs by organ [
27], including other carcinomas [
28], and future analysis of the efficacy of second-line therapy in patients with progression of extrahepatic lesions after ICIs as first-line therapy is also warranted.
Therefore, if the therapeutic effect of atezolizumab plus bevacizumab is judged to be poor, it may be better to change to lenvatinib immediately. As a way to examine the effects of atezolizumab plus bevacizumab at an early stage, there is a report that decreased AFP in unresectable HCC patients treated with atezolizumab plus bevacizumab at 3 weeks was identified as a factor predicting early tumor response [
29]. This would help determine whether to continue atezolizumab plus bevacizumab at an early stage.
Recently, the results of phase III HIMALAYA trial which evaluated single tremelimumab, regular interval durvalumab (STRIDE) as first-line standard systemic therapy for unresectable HCC were published. As a result, STRAIDE showed significantly better efficacy compared to sorafenib [
30]. Then, we have to consider whether to use STRIDE for second-line treatment of patients who received atezolizumab plus bevacizumab as first-line treatment. Although in other cancer types, in the treatment of renal cell carcinoma patients with disease progression during or after treatment with ICIs, the combination therapy with atezolizumab and cabozantinib as a TKI did not improve PFS or OS compared with cabozantinib alone and was associated with an increase in serious AEs [
31]. Considering AEs, this may be a factor in the choice of treatment with lenvatinib and other TKIs as second-line therapy after atezolizumab plus bevacizumab.
The present study has two limitations. First, it was retrospective. Second, a selection bias could have existed because of the clinical observational nature of the study. Nevertheless, the usefulness of lenvatinib after atezolizumab plus bevacizumab was demonstrated. We believe that this information will be very useful for the systemic therapy of patients with unresectable HCC. Further accumulation of evidence is expected to establish an effective treatment regimen after atezolizumab plus bevacizumab combination therapy.
Author Contributions
Conceptualization, S.Y., T.K., Y.S., R.M., K.A., K.N., K.Y., S.U. and M.T.; Formal Analysis, S.Y.; Data Curation, S.Y., T.K., S.Y., Y.J., M.K., Y.S., R.M., K.A., K.N., K.Y., Y.F., S.U., H.F., A.O., T.N., E.M., D.M., M.T., Y.T., H.K., S.T., N.M., K.T. and S.O. Supervision, T.K. M.T. and S.O.; Writing—Original Draft, S.Y.; Writing—Review and Editing, T.K. and M.T. All authors have read and agreed to the published version of the manuscript.