Atezolizumab (anti-programmed death-ligand 1; anti-PD-L1) in conjunction with bevacizumab (anti-vascular endothelial growth factor; anti-VEGF) has become the established standard first-line systemic treatment for unresectable hepatocellular carcinoma (HCC). Despite an improved objective response rate (ORR) of 27%, the majority of patients face HCC progression and liver failure [Finn et al., N Engl J Med 2020]. Developing a new combined treatment strategy to overcome resistance to anti-PD-L1 and anti-VEGF is essential to improve patient outcomes.

Radiation treatment (RT) is notably effective in managing localized solid tumors and is a fundamental component of unresectable HCC treatment. Recent retrospective cohorts have demonstrated that proton RT targeting all hepatic tumors, along with PD-L1/programmed death-1 (PD-1) blockade, enhances ORR and progression-free survival for unresectable HCC patients, displaying a favorable safety profile (Su et al., Am J Cancer Res. 2022). Our preclinical study (Hsieh et al., Sci Immunol 2022) showcased that RT combined with PD-L1/PD-1 blockade stimulates immunogenic cell death and antigen cross-presentation in murine tumor models, promoting systemic antitumor T cell responses. Nonetheless, it is crucial to verify whether the combined therapy of proton RT, atezolizumab, and bevacizumab triggers synergistic antitumor effects and systemic immune activation in clinical trials for unresectable HCC. This phase II non-randomized trial aims to prospectively evaluate therapeutic efficacy, safety, and immunological responses in patients with unresectable HCC treated with atezolizumab/bevacizumab combined with proton radiotherapy.

Inclusion Criteria:

• Participants must have diagnosis of HCC that is deemed unsuitable for surgical resection or transplant. Participants may have multiple lesions with a total maximal tumor dimension of < 20 cm, and no one lesion > 15 cm. Diagnosis should be confirmed by at least 1 criterion listed below:

  • Histologically or cytologically proven diagnosis of HCC.
  • Typical arterial enhancement and delayed washout on multiphasic CT or MRI.

• Age ≥18 years at the time of signing informed consent document.

• ECOG performance status 0-1.

• Barcelona Clinic Liver Cancer (BCLC) stages Intermediate (B) or Advanced (C).

• Child-Pugh score 5-6 liver function within 28 days of study registration.

• Documented virology status of hepatitis B virus (HBV), as confirmed by screening HBV serology test.

• Documented virology status of hepatitis C virus (HCV), as confirmed by screening HCV serology test.

• Ability to understand and the willingness to sign a written informed consent document

• Adequate bone marrow, liver, and renal function within 4 weeks before study registration

  • Hemoglobin ≥ 9.0 g/dL
  • Absolute neutrophil count (ANC) ≥ 1,000/mm3
  • Platelet count ≥ 50,000/μL
  • Total bilirubin < 2.5 mg/dL
  • Serum albumin >2.8 g/dL
  • Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 × upper limit of normal (ULN)
  • Prothrombin time ≤ 6 seconds prolonged
  • Serum creatinine ≤ 1.5 mg/dL

Exclusion Criteria:

• Prior invasive malignancy unless disease free for a minimum of 2 years

• Prior radiotherapy to the region of the liver that would result in overlap of radiation therapy fields

• Prior selective internal radiotherapy/hepatic arterial yttrium therapy, at any time

• Untreated active hepatitis B or hepatitis C

• Moderate to severe or intractable ascites

• Presence of distant metastases that cannot be encompassed by proton radiotherapy

• Untreated or incomplete treated esophageal or gastric varices

• Severe, active co-morbidity, defined as follows:

  • Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months prior to registration
  • Myocardial infarction within the last 6 months prior to study entry
  • Acute bacterial or fungal infection requiring intravenous antibiotics within 28 days prior to study entry
  • A bleeding episode within 6 months prior to study entry due to any cause.
  • Thrombolytic therapy within 28 days prior to study entry.
  • Known bleeding or clotting disorder.
  • Uncontrolled psychotic disorder

• Pregnancy or women of childbearing potential and men who are sexually active and not willing/able to use medically acceptable forms of contraception

• Prior solid organ transplantation.

• Prior or active autoimmune disease (AID) including autoimmune hepatitis, inflammatory bowel disease, myasthenia gravis, systemic lupus erythematosus, rheumatoid arthritis, antiphospholipid antibody syndrome, Wegener granulomatosis, Sjogren's syndrome, Guillain-Barre syndrome, and multiple sclerosis.

• Prior or active thrombotic or bleeding disorders, hemoptysis, cerebral vascular accident, significant cardiac disease (ischemic or congestive heart failure), or gastrointestinal perforation.

• Inability to treat all sites of disease by proton radiotherapy (such as extrahepatic metastases or massive liver tumors whereby the liver constraints [ULV/SLV >40%] cannot be met for covering all sites of liver tumors using proton radiotherapy.)

• Known HIV infection.

Sharing individual participant data (IPD) with other researchers requires IRB review and approval. Presently, we do not have a plan to provide IPD to other researchers.