Clinical application of a programmed death ligand-1 inhibitor combined with low-dose pulsed radiotherapy in recurrent metastatic hepatocellular carcinoma

Abstract

BACKGROUND

Hepatocellular carcinoma (HCC) is among the malignancies with the poorest prognosis. The first-line standard treatment for recurrent metastatic HCC achieves an objective response rate of only approximately 30%, with a median progression-free survival (PFS) of approximately 6 months. The efficacy of second-line and subsequent therapies is even more limited.

AIM

To investigate the efficacy and safety of a programmed death ligand-1 inhibitor combined with low-dose pulsed radiotherapy in patients with recurrent metastatic HCC.

METHODS

Patients with confirmed advanced primary HCC who experienced disease progression following at least one prior line of therapy were enrolled. A low-dose pulsed radiotherapy regimen was administered, consisting of 0.2 Gy per pulse delivered at 3-minute intervals, with 10 fractions per day over 5 consecutive days per week. One week after the initiation of radiotherapy, intravenous atezolizumab (1200 mg every 3 weeks) was added. Efficacy was evaluated after 2 cycles of atezolizumab according to the response evaluation criteria in solid tumors 1.1 criteria. Peripheral blood T-lymphocyte subsets were analyzed before treatment and after the completion of pulsed radiotherapy plus 2 cycles of atezolizumab.

RESULTS

Patient A eventually had a PFS of 4.7 months and an overall survival (OS) of 7.7 months. Patients B and C are still under follow-up (March 2026) and remain well controlled without progression. The PFS and OS of patient B exceeded 15 months, and the PFS and OS of patient C exceeded 8 months. Patient D was the only progressive case, with an OS of only 2.2 months. According to peripheral blood T lymphocyte subset analysis, the percentage of programmed death 1-positive T lymphocytes in patients A, B, and C remained low or even decreased, whereas the percentage of programmed death 1-positive T lymphocytes in patient D significantly increased after treatment. Conversely, the ratio of CD8⁺ terminally differentiated effector T cells/cytotoxic T lymphocytes in patients A, B, and C was greater than the ratio of CD8⁺ effector memory T cells/cytotoxic T lymphocytes, whereas the opposite was true for patient D.

CONCLUSION

A programmed death ligand-1 inhibitor combined with low-dose pulsed radiotherapy achieved clear efficacy in some patients, with good safety and tolerability.

Key Words: Programmed death ligand-1 inhibitor; Pulsed radiotherapy; Hepatocellular carcinoma; Clinical application; T lymphocyte subsets

Core Tip: The combination of a programmed death ligand-1 inhibitor (atezolizumab) and low-dose pulsed radiation therapy has shown good efficacy and safety in some patients with recurrent metastatic hepatocellular carcinoma.

INTRODUCTION

Hepatocellular carcinoma (HCC) is among the malignancies with the poorest prognosis. The objective response rate (ORR) of first-line standard treatment for recurrent metastatic HCC is only approximately 30%, with a median progression-free survival (PFS) of approximately 6 months[1]. The efficacy of second-line and subsequent treatments is even worse. Furthermore, recurrent metastatic HCC can cause local compression of the bile ducts or portal vein, leading to symptoms such as jaundice, portal hypertension, and pain, which severely affect patient survival and quality of life. These patients often have poor general condition and impaired liver function, making them unable to tolerate conventional radiotherapy and other local treatment modalities. This condition necessitates new local interventions and later-line systemic therapies. In this study, we used low-dose pulsed radiotherapy because of its efficient and safe nature to irradiate local lesions in advanced HCC patients, alleviating local symptoms and fully protecting the liver and other organs. Moreover, this study combines this approach with programmed death ligand-1 (PD-L1) inhibitor therapy to overcome the radiotherapy-induced upregulation of PD-L1[2] while leveraging the systemic effects of the PD-L1 inhibitor to improve treatment outcomes for previously treated recurrent metastatic HCC.

MATERIALS AND METHODS

Inclusion and exclusion criteria

Inclusion criteria: (1) A confirmed diagnosis of primary HCC and advanced-stage disease; (2) No contraindications for radiotherapy and immunotherapy, with a Karnofsky Performance Status score ≥ 60; (3) Expected survival ≥ 3 months; and (4) Disease progression after at least one line of treatment.

Exclusion criteria: (1) Psychiatric disorders, severe hepatic, renal, cardiac, pulmonary, or other major organ dysfunction, or other serious diseases; (2) Severe infection and bone marrow suppression that cannot be corrected; (3) Pregnancy or breastfeeding; and (4) History of allergies or hypersensitivity to multiple drugs.

Radiotherapy

The following equipment and parameters were used: A medical Varian IGIT linear accelerator, eclipse planning system, three-dimensional conformal/intensity-modulated radiotherapy techniques, 6 MV X-rays, irradiation distance of 100 cm, dose rate of 100 MU/minute, low-dose pulsed radiotherapy mode, single irradiation dose of 0.2 Gy, irradiation pulse interval of 3 minutes, 10 fractions/day, total daily dose of 2 Gy, and irradiation for 5 days per week. All patients in this study had recurrent metastatic HCC and were receiving later-line palliative therapy. Palliative radiotherapy typically involves a total dose of 30-50 Gy. Due to the large size of the lesion, patient D received 50 Gy.

Combination with PD-L1 inhibitor

Intravenous atezolizumab (Tecentriq) was administered one week after the start of radiotherapy at a dose of 1200 mg per infusion every 3 weeks.

Efficacy evaluation

Short-term efficacy was evaluated after 2 cycles of atezolizumab, in which the response evaluation criteria in solid tumors 1.1 were used to compare changes in tumor lesion size before and after treatment. Responses were categorized as complete response (CR), partial response (PR), stable disease (SD), and progressive disease. The ORR was calculated as CR + PR, and the disease control rate (DCR) was defined as CR + PR + SD.

PFS and overall survival (OS) were assessed on the basis of the patient’s general condition, complete blood count, liver and kidney function, electrocardiogram, chest computed tomography (CT), and enhanced upper abdominal CT scans during treatment. The start date for both PFS and OS was the first day of radiotherapy. Patients were followed up at least once a month via telephone to gather information.

Toxicities

The National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0 were applied to classify toxicity into severity grades 1-5. Common adverse events during treatment were monitored, including anemia, leukopenia, thrombocytopenia, impaired liver function, vomiting, diarrhea, rash, hepatitis, pneumonia, and nephritis.

Correlative factor analysis

Peripheral blood T lymphocyte subsets were analyzed before treatment and after pulsed radiotherapy + 2 cycles of atezolizumab to determine the impact of pulsed radiotherapy combined with a PD-L1 inhibitor on the immune microenvironment of primary HCC.

RESULTS

Four patients were included in the analysis. The efficacy and outcome in these patients were as follows (Table 1, Figure 1).

Figure 1  Efficacy evaluation after pulsed radiotherapy and 2 cycles of atezolizumab.

Table 1 Peripheral blood T lymphocyte subset analysis.

Patient	Pre-treatment (%)	After pulse radiotherapy and 2 cycles of atezolizumab (%)
Patient A
PD-1+ T cells/T cells	2.13	0.80
PD-1+ helper T cells/helper T cells	2.31	0.43
PD-1+ cytotoxic T cells/cytotoxic T cells	1.67	0.90
CD8+ terminally differentiated effector T cells/cytotoxic T cells	39.29	42.71
CD8+ effector memory T cells/cytotoxic T cells	34.47	50.57
Patient B
PD-1+ T cells/T cells	1.16	0.40
PD-1+ helper T cells/helper T cells	0.97	0.37
PD-1+ cytotoxic T cells/cytotoxic T cells	1.55	0.33
CD8+ terminally differentiated effector T cells/cytotoxic T cells	55.52	38.24
CD8+ effector memory T cells/cytotoxic T cells	22.27	21.59
Patient C
PD-1+ T cells/T cells	0.04	0.22
PD-1+ helper T cells/helper T cells	0.03	0.19
PD-1+ cytotoxic T cells/cytotoxic T cells	0.05	0.15
CD8+ terminally differentiated effector T cells/cytotoxic T cells	40.11	55.15
CD8+ effector memory T cells/cytotoxic T cells	31.94	25.37
Patient D
PD-1+ T cells/T cells	1.24	4.92
PD-1+ helper T cells/helper T cells	1.29	9.08
PD-1+ cytotoxic T cells/cytotoxic T cells	1.29	2.94
CD8+ terminally differentiated effector T cells/cytotoxic T cells	13.09	17.10
CD8+ effector memory T cells/cytotoxic T cells	32.09	70.39

PD-1: Programmed death 1.

Patient A was a 61-year-old male with a history of hepatitis B. The CT scan, performed on October 17, 2024, revealed disease progression after multiple lines of treatment, and the patient entered the study group. Pulsed radiotherapy to liver lesions was initiated on October 30, 2024, for a total dose of 30 Gy, combined with atezolizumab. A CT scan performed on December 17, 2024 revealed SD. Immune maintenance therapy was continued. The disease progressed on March 20, 2025, and the patient died on June 20, 2025. The PFS was 4.7 months, and the OS was 7.7 months.

Patient B was a 53-year-old male with a history of hepatitis C. A CT scan performed on November 25, 2024, revealed disease progression after first-line treatment, and the patient entered the study group. Pulsed radiotherapy to liver lesions was initiated on December 4, 2024, for a total dose of 30 Gy combined with atezolizumab. CT performed on January 20, 2025, revealed SD. Immune maintenance therapy was continued, and follow-up is ongoing. PFS and OS have not yet been reported.

Patient C was a 59-year-old male with a history of hepatitis B. A CT scan performed on June 30, 2025, revealed disease progression after second-line treatment, and the patient entered the study group. Pulsed radiotherapy to liver lesions was initiated on July 7, 2025, for a total dose of 30 Gy combined with atezolizumab. CT performed on August 26, 2025, revealed a PR. Immune maintenance therapy was continued, and follow-up is ongoing. PFS and OS have not yet been reported.

Patient D was a 53-year-old male with a history of hepatitis B. A CT scan performed on December 2, 2025, revealed disease progression after multiple lines of treatment, with an AFP concentration > 1000 ng/mL. The patient entered the study group. Pulsed radiotherapy to liver lesions was initiated on December 10, 2025, for a total dose of 50 Gy combined with 2 cycles of atezolizumab. CT performed on January 28, 2026, revealed progressive disease, and the patient died on February 16, 2026. The OS was 2.2 months.

DISCUSSION

The RESORCE study was a phase III clinical trial evaluating regorafenib as a second-line treatment for advanced HCC[3]. In this study, 573 HCC patients with Child-Pugh A liver function for whom first-line therapy failed were randomized to either the regorafenib or placebo arm. Compared with placebo, regorafenib significantly prolonged the median OS (mOS) (10.6 months vs 7.8 months) and median PFS (mPFS) (3.1 months vs 1.5 months) and improved the ORR (11% vs 4%) and DCR (65% vs 36%). Consequently, regorafenib was approved by the Food and Drug Administration and National Medical Products Administration for the second-line treatment of advanced HCC. The KEYNOTE-224 study[4] was a single-arm, open-label, international multicenter phase II clinical trial evaluating pembrolizumab as a second-line treatment for advanced HCC. A total of 104 advanced HCC patients who had progressed on or were intolerant to sorafenib were enrolled. The ORR was 17%, the mPFS was 4.9 months, and the mOS was 12.9 months. The KEYNOTE-394 study was a randomized, double-blind, international multicenter phase III clinical trial conducted in the Asia-Pacific region (NCT03062358) that evaluated pembrolizumab or placebo combined with best supportive care in advanced HCC patients who had previously received sorafenib or oxaliplatin-based chemotherapy. Eighty-five percent of the patients were from China[5,6]. The primary endpoint was OS, and the secondary endpoints included PFS, ORR, DCR, and safety. Pembrolizumab significantly prolonged mOS (14.6 months vs 13.0 months) compared with the control, reaching the pre-defined statistical endpoint. Two secondary endpoints, mPFS (2.6 months vs 2.3 months) and ORR (12.7% vs 1.3%), were also statistically significant. Data from the KEYNOTE-224 and KEYNOTE-394 studies support the use of pembrolizumab as a second-line treatment for advanced HCC. The CELESTIAL study (NCT01908426)[7,8] was a randomized, placebo-controlled, international multicenter phase III clinical trial enrolling patients with HCC who had previously received sorafenib and had progressed after at least one line of systemic therapy to receive cabozantinib or placebo. Cabozantinib significantly prolonged mOS (10.2 months vs 8.0 months; P = 0.005) and mPFS (5.2 months vs 1.9 months; P < 0.001), with ORRs of 4% and < 1% (P = 0.009), respectively. Cabozantinib was approved by the Food and Drug Administration for the second-line treatment of advanced HCC. The RATIONALE-208 study was a single-arm, open-label, international multicenter phase II clinical trial (NCT03419897) evaluating tislelizumab for patients with unresectable HCC who had previously received at least one systemic treatment[9]. The mOS was 13.2 months, the mPFS was 2.7 months, the Independent Review Committee-assessed ORR was 13.3%, and the DCR was 53.0%. On the basis of these results, the National Medical Products Administration conditionally approved tislelizumab for treating patients with HCC who have undergone at least one systemic treatment. AHELP was a randomized, double-blind, parallel-controlled, multicenter phase III clinical study of apatinib mesylate tablets as a second-line or later-line treatment for advanced HCC patients[10]. The study enrolled advanced HCC patients who had previously failed or were intolerant to at least one line of systemic treatment. The mOS was 8.7 months and 6.8 months, and the mPFS was 4.5 months and 1.9 months, respectively, for the apatinib and placebo groups. Apatinib significantly prolonged mOS (hazard ratio = 0.785; P = 0.0476) and mPFS (hazard ratio = 0.471; P < 0.0001). In the apatinib group, the ORR and DCR was 10.7% and 61.3%, respectively, compared with only 1.5% and 28.8% in the placebo group.

Most of the drugs currently approved for second-line treatment of HCC are based on studies of patients who had failed in sorafenib and/or oxaliplatin-based systemic chemotherapy. With the increasing use of novel molecularly targeted drugs, such as lenvatinib, donafenib, and immune checkpoint inhibitors, as the first-line treatment, the optimal second-line treatment strategy for patients who have progressed on first-line lenvatinib, donafenib, immunotherapy monotherapy, or immunotherapy combination therapy remains unclear, and there remains a lack of sufficient, high-level evidence-based medicine. The patient’s wishes, performance status, underlying liver diseases, and mode of disease progression should be comprehensively considered.

Pulsed radiation therapy is an innovative radiotherapy modality that effectively controls lesions while minimizing radiation damage to adjacent normal tissues and organs. It utilizes the principle of low-dose hyper-radiosensitivity, which refers to the phenomenon in which low-dose radiation exerts a stronger cell-killing effect compared with the extrapolated value predicted by the traditional linear-quadratic model. Compared with normal tissue cells, proliferative malignant tumor cells exhibit more pronounced low-dose hyper-radiosensitivity, allowing the achievement of greater therapeutic efficacy with lower radiation doses. Additionally, due to the short fixed time intervals between successive low-dose irradiations in pulsed radiation therapy, the repair of sublethal damage in normal tissue cells is promoted, thereby reducing radiotherapy-related side effects in normal tissues[11,12]. Multiple studies have confirmed the efficacy and safety of pulsed radiotherapy[13-17].

In the RESORCE, KEYNOTE-224, KEYNOTE-394, CELESTIAL, RATIONALE-208, and AHELP studies, the mPFS for second-line HCC treatment ranged from 2.6 months to 5.2 months, the mOS ranged from 8.7 months to 14.6 months, the ORR ranged from 4% to 17%, the DCR ranged from 53.0% to 65%, and the overall efficacy was limited. In the present study, patient A achieved a PFS of more than 4 months and an OS of more than 6 months, even after multiline treatment. Patients B and C received second-line and third-line treatments, respectively, and the disease has been well controlled without progression to date. In terms of safety, no adverse reactions, such as fatigue, nausea, vomiting, decreased appetite, diarrhea, bone marrow suppression, abnormal liver function, or impaired renal or pancreatic function, were observed during radiotherapy or combined immunotherapy, and patients tolerated the treatment well.

According to peripheral blood T lymphocyte subset analysis, compared with that before treatment, the percentage of programmed death 1 (PD-1)-positive T lymphocytes in patients A, B, and C was maintained at a low level or even decreased after treatment with pulsed radiotherapy + 2 cycles of atezolizumab, while the percentage of PD-1-positive T lymphocytes in patient D significantly increased after treatment. The PD-1-positive T lymphocytes/T lymphocytes, PD-1-positive helper T lymphocytes/helper T lymphocytes, and PD-1-positive cytotoxic T lymphocytes/cytotoxic T lymphocytes increased to 4.92%, 9.08%, and 2.94%, respectively. Conversely, the ratio of CD8⁺ terminally differentiated effector T cells/cytotoxic T lymphocytes in patients A, B, and C was greater than the ratio of CD8⁺ effector memory T cells/cytotoxic T lymphocytes, whereas the opposite was true for patient D, where the percentage of CD8⁺ terminally differentiated effector T cells was significantly lower than that of CD8⁺ effector memory T cells.

There are limitations in this study. With only four patients included, any statistical inference would be unreliable, and the risk of selection bias and chance findings is high. Therefore, no formal statistical comparisons were performed, and our observations should be considered preliminary and descriptive. A larger, prospective study with appropriate power calculations is necessary to confirm these findings and to assess generalizability.

CONCLUSION

PD-L1 inhibitors combined with low-dose pulsed radiotherapy achieved clear efficacy in some HCC patients, with good safety and tolerability. These preliminary observations suggest that pulsed radiotherapy combined with immunotherapy may be feasible and warrants further investigation in a larger cohort.