Abstract
Keywords
Introduction
Hepatocellular carcinoma (HCC) is the most dominant type of primary liver cancer, accounting for up to 90% of primary liver malignancies; it represents the sixth most prevalent and the third most fatal human cancer worldwide, contributing over 800 000 new cases and 700 000 new deaths annually.1,2 Various therapeutic strategies have been developed for the treatment of HCC patients, including surgical therapy (such as liver resection and transplantation), 3 locoregional therapy (such as radiation, ablation, and embolization), 4 systemic therapy (such as chemotherapy and molecular targeted therapy), 5 and immunotherapy (such as chimeric antigen receptor T cell therapy and immune checkpoint blockade). 6 However, the survival benefits of these therapeutic options for HCC patients still need to be improved. Therefore, the identification of valuable prognostic biomarkers for the outcomes of HCC patients is vital for the early detection and timely management of patients with poor prognosis to aid in their survival.
As a combination of immunotherapeutic agents and molecular targeted agents, atezolizumab (an anti-programmed death ligand 1 (PD-L1) antibody) plus bevacizumab (an anti-vascular endothelial growth factor (VEGF) antibody) have been approved by the United States Food and Drug Administration (FDA) as a new first-line systemic therapy for the treatment of patients with unresectable HCC in 2020.7,8 Compared with sorafenib, the first systemic therapy to be approved for unresectable HCC in the first-line setting, the results of a phase 3 IMbrave150 trial demonstrated that atezolizumab plus bevacizumab combination therapy had improved the median overall survival (OS: 19.2 months vs 13.4 months) and progression-free survival (RFS: 6.9 months vs 4.3 months) as well as showing a better objective response rate (ORR: 29.8% vs 11.3%) and complete response rate (7.7% vs 0.6%).9,10 The superior efficacy of atezolizumab plus bevacizumab combination therapy is attributed to the direct effect of bevacizumab, which enables efficient priming and activation of T cell responses, normalizes tumor vasculature to increase T cell recruitment, and reprograms the tumor microenvironment from being immune suppressive to immune permissive, in addition to its synergistic effect with atezolizumab, which restores T cell-mediated tumor cell killing.11,12 However, there remains an urgent need for biomarkers to predict the prognosis of HCC patients receiving atezolizumab plus bevacizumab combination therapy.
Considering that atezolizumab plus bevacizumab has replaced sorafenib as a more powerful first-line systemic therapy for unresectable HCC, this review comprehensively summarizes the evidence in the literature validating the prognostic significance of a single or a combination of biomarker(s) in tissue, whole blood, serum, plasma, or urine specimens of HCC patients at pre-treatment or in-treatment time points of atezolizumab plus bevacizumab combination therapy.
Single Prognostic Biomarkers for HCC Patients Treated with Atezolizumab plus Bevacizumab Combination Therapy
Prognostic Biomarkers for HCC Patients Treated With Atezolizumab Plus Bevacizumab Combination Therapy.
aOS was defined as the time from treatment initiation to death due to any cause. PFS was defined as the time from treatment initiation to radiological progression or death due to any cause. TTP was defined as the time from treatment initiation to radiological progression (but not death) due to any cause.
bAFP ratio was calculated by dividing the level of AFP at 3 weeks after treatment initiation by pre-treatment level.
cAFP decrease was defined as reduction in serum AFP levels at 6 weeks after treatment initiation relative to pre-treatment levels.
dAFP decrease and increase were defined as reduction and elevation in serum AFP levels at 6 weeks after treatment initiation relative to pre-treatment levels, respectively.
eChange in AFP level was stratified into three distinct trajectories. In the sharp-falling group, pre-treatment AFP level declined from ≥ 100 ng/mL toward the range (0-20 ng/mL) within 4 months after treatment initiation. In the high-rising group, AFP increased from an elevated pre-treatment level (>100 ng/mL) toward a higher level. In the low-stable group, pre-treatment AFP level < 100 ng/mL decreased and remained below 20 ng/mL.
fIL-6 level was detected at 3 weeks after treatment initiation.
gThe ratio of IL-10 and TNF-α was calculated by dividing their level at 3 weeks after treatment initiation by pre-treatment level.
hCXCL10 level was detected at 3 weeks after treatment initiation.
iAnti-PD-1 autoantibody level was defined as the ratio relative to the lowest level of anti-PD-1 autoantibodies in 63 healthy volunteers.
jEV size was detected at 3 weeks after treatment initiation. Change in EV size was detected at 9 weeks after treatment initiation and relative to pre-treatment size.
kThe level of PD1+ granulocytes was defined as their percentage in total white blood cells and was categorized as high or low level based on their mean percentage as a cut off.
lNLR was calculated by dividing blood neutrophil count by blood lymphocyte count.
mThe level of CD8+PD-1+Ki-67+ T cells and CD4+Foxp3+PD-1+LAG3+ T cells was defined as their percentage in total peripheral blood mononuclear cells.
nThe level of CD8+ central memory T cells was defined as their percentage in total peripheral blood mononuclear cells. Change in CD8+ central memory T cell level was detected at 3 weeks after treatment initiation and relative to pre-treatment size.
oPNI was defined as serum albumin level (g/dL) multiplied by 10 plus peripheral lymphocyte count per μL multiplied by 0.005.
pPNI was detected at 3 weeks after treatment initiation.
qGrade ≥ 2 proteinuria was defined as a urine protein–creatinine ratio of ≥ 2.0 g/g creatinine.
rAFP decrease was defined as reduction in serum AFP levels at 3 weeks after treatment initiation relative to pre-treatment levels. ALBI grade was defined as log10 serum bilirubin level (mg/dL) multiplied by 0.66 plus serum albumin level (g/dL) multiplied by −0.085 and was stratified as grade 1 (≤−2.60), 2 (>−2.60 to ≤ −1.39), or 3 (>−1.39). No patients were ALBI grade 3 in the analysis.
smALBI grade was calculated by the same formula as ALBI grade and stratified as grade 1 (≤−2.60), grade 2a (>−2.60 to ≤ −2.27), grade 2b (>−2.27 to ≤ −1.39), or grade 3 (>−1.39).
tAFP, mALBI grade, BCLC staging, and DCP score was calculated as the summation of points from AFP (<100 and ≥ 100 ng/mL as points 0 and 1, respectively), mALBI (1, 2a, and 2b/3 as points 0, 1, and 2), BCLC (0/A/B and C/D as points 0 and 1, respectively), and DCP (<100 and ≥ 100 mAU/mL as points 0 and 1, respectively) and was categorized as 0 point, 1 point, 2 points, 3 points, 4 points, or 5 points.
uAFP, CRP, and NLR score was defined as 1.62 minus 0.38 multiplied by log10 serum AFP level (mg/mL) minus 0.61 multiplied by serum CRP level (mg/dL) minus 0.37 multiplied by NLR.
vIGF-1, albumin, bilirubin, and prothrombin prolongation time score was calculated as the summation of points from IGF-1 (>50, 26-50, and < 26 ng/mL as points 1, 2, and 3, respectively), albumin (>3.5, 2.8-3.5, and < 2.8 g/dL as points 1, 2, and 3, respectively), bilirubin (<2, 2-3, and > 3 mg/dL as points 1, 2, and 3, respectively), and prothrombin prolongation time (<4, 4-6, and > 6 seconds as points 1, 2, and 3, respectively) and was categorized as 4-5 points, 6-7 points, or > 7 points.
wThe level of PD1-CD45RA+CD8+ effector memory T cells and PD-L1+CXCL10+ macrophages was defined as their density in tumor tissues and was categorized as high or low level based on their respective median densities as a cut off.
xPD-L1+ tumor cell and PD-L1+ tumor-infiltrating cell score was calculated by summing the number of PD-L1+ tumor cells and the number of PD-L1+ tumor-infiltrating cells and then dividing that total by the overall number of tumor cells, with a maximum score of 100.
Abbreviations: HCC, hepatocellular carcinoma; AFP, α-fetoprotein; ELISA, enzyme-linked immunosorbent assay; PFS, progression-free survival; OS, overall survival; CRP, C-reactive protein; DCP, des‐gamma‐carboxy prothrombin; OPN, osteopontin; IL, interleukin; CLEIA, chemiluminescence enzyme immunoassay; TNF-α, tumor necrosis factor-α; CXCL, C-X-C motif chemokine ligand; IGF-1, insulin-like growth factor-1; LAG-3, lymphocyte-activation gene 3; PD-1, programmed death 1; TERT, telomerase reverse transcriptase; ctDNA, circulating tumor DNA; NGS, next-generation sequencing; EV, extracellular vesicle; NTA, nanoparticle tracking analysis; TTP, time to progression; NLR, neutrophil-to-lymphocyte ratio; Foxp3, forkhead box protein 3; CTC, circulating tumor cell; EpCAM, epithelial cell adhesion molecule; TGF-β, transforming growth factor-β; NA, not applicable; MRI, magnetic resonance imaging; APHE, arterial phase hyperenhancement; PNI, prognostic nutritional index; ALBI, albumin–bilirubin; mALBI, modified ALBI; BCLC, Barcelona Clinic Liver Cancer; PD-L1, programmed death ligand 1; scRNAseq, single-cell RNA sequencing; IHC, immunohistochemistry.
Combination Prognostic Biomarkers for HCC Patients Treated with Atezolizumab plus Bevacizumab Combination Therapy
In addition to single biomarkers, the prognostic significance of several combination biomarkers in HCC patients receiving atezolizumab plus bevacizumab combination therapy has been validated in multiple lines of studies (Table 1). The study conducted by Campani et al. carried out ELISA to detect the pre-treatment albumin–bilirubin (ALBI) grade and the in-treatment decrease in the serum AFP levels at 3 weeks after treatment initiation, as combination biomarkers, to stratify 70 retrospectively enrolled patients with unresectable HCC and revealed that patients with an AFP decrease (≤20%) combined with a high ALBI grade (grade 2) had the shortest OS and PFS. 44 By conducting ELISA to measure the pre-treatment serum AFP levels and modified ALBI (mALBI) grade as combination biomarkers, Hatanaka et al. stratified 426 retrospectively enrolled patients with unresectable HCC and demonstrated that patients with a high AFP level (≥100 ng/mL) combined with a high mALBI grade (grade 2b/3) had the shortest OS and PFS. 45 The study conducted by Ohama et al. performed ELISA and combined the pre-treatment serum levels of AFP (<100 and ≥ 100 ng/mL scored with points 0 and 1, respectively) and DCP (<100 and ≥100 mAU/mL scored with points 0 and 1, respectively), mALBI grade (1, 2a, and 2b/3 scored with points 0, 1, and 2), and BCLC staging (0/A/B and C/D scored with points 0 and 1, respectively) in a scoring system to stratify 719 retrospectively enrolled patients with unresectable HCC and verified that patients with the highest summation score (5 points) had the shortest OS and PFS. 46 Based on ELISA analysis of the pre-treatment serum levels of AFP and CRP as combination biomarkers, Hatanaka et al. stratified 297 retrospectively enrolled patients with unresectable HCC and determined that patients with a high AFP level (≥100 ng/mL) combined with a high CRP level (≥1 mg/dL) had the shortest OS and PFS. 47 The study conducted by Ueno et al. used ELISA and flow cytometry to detect and combine the pre-treatment serum levels of AFP, CRP, and NLR in a scoring system to stratify 119 retrospectively enrolled patients with unresectable HCC and found that patients with high AFP, CRP, and NLR scores (≥0) had longer OS and PFS. 48 Using ELISA-based measurement of the pre-treatment serum CRP levels and ALBI grade as combination biomarkers, Tada et al. stratified 421 retrospectively enrolled patients with unresectable advanced HCC and ascertained that patients with a high CRP level (>1 mg/dL) combined with a high ALBI grade (grade 2/3) had the shortest OS and PFS. 49 The study conducted by Kaseb et al. carried out ELISA and combined the pre-treatment serum levels of IGF-1 (>50, 26-50, and < 26 ng/mL scored with points 1, 2, and 3, respectively), albumin (>3.5, 2.8-3.5, and < 2.8 g/dL scored with points 1, 2, and 3, respectively), bilirubin (<2, 2-3, and > 3 mg/dL scored with points 1, 2, and 3, respectively), and the prothrombin prolongation time (<4, 4-6, and > 6 seconds scored with points 1, 2, and 3, respectively) in a scoring system to stratify 256 prospectively enrolled patients with unresectable advanced HCC and validated that patients with the lowest summation score (4-5 points) had the longest OS and PFS. 27 The study conducted by Cappuyns et al. conducted single-cell RNA sequencing (scRNAseq) to analyze the pre-treatment levels of PD-1-CD45RA+CD8+ effector memory T cells and PD-L1+CXCL10+ macrophages in tumor tissues as combination biomarkers to stratify 253 prospectively enrolled patients with unresectable advanced HCC and determined that patients with a high PD-1-CD45RA+CD8+ effector memory T cell level combined with a high PD-L1+CXCL10+ macrophage level had the longest OS and PFS. 50 Lee et al. performed immunohistochemistry (IHC) staining to detect and combine the pre-treatment levels of PD-L1+ tumor cells and PD-L1+ tumor-infiltrating cells in tumor tissues in a scoring system to stratify 72 retrospectively enrolled patients with unresectable HCC and showed that patients with a high PD-L1+ tumor cell and PD-L1+ tumor-infiltrating cell score (≥10) predicted a longer OS and PFS. 51
Conclusions
This review provided a comprehensive summary of the evidence in the literature validating the prognostic significance of a variety of a single or a combination biomarker(s) in different sampling sources at different sampling time points in HCC patients receiving atezolizumab plus bevacizumab combination therapy. These prognostic biomarkers hold great potential in identifying the HCC patients with poor outcomes after atezolizumab plus bevacizumab combination therapy for earlier diagnosis and better treatment to improve their survival. When a patient is stratified as the high-risk population based on the prognostic threshold of specific biomarkers detected in the indicated specimens at the pre-treatment or the indicated in-treatment time points, the medical follow-ups after therapy can be arranged more frequently for the patient to monitor the health status and disease progression and ensure the patient to receive timely healthcare and treatment management. Most of the current biomarkers for atezolizumab plus bevacizumab combination therapy in HCC patients, including protein-based, nonprotein-based, and immune cell biomarkers, are derived from liquid biopsies such as whole blood, serum, plasma, and urine, highlighting the convenience and safety of using noninvasive sampling sources in clinical application. In addition, some biomarkers are derived from the MRI imaging of tumor nodule numbers and pathological features, as well as treatment-related adverse events, in a noninvasive manner with no need for sampling. Other biomarkers are derived from the profiling of tumor cells and immune cell subpopulations in tumor tissues. Moreover, many biomarkers are based on cytokines, immune-related proteins, or immune cells, suggesting the clinical implication of the tumor immune microenvironment in the treatment efficacy of atezolizumab plus bevacizumab combination therapy in HCC patients. In clinical practice, ELISA is considered a cost-, time-, and labor-effective method applied in biomarker detection compared with NGS, scRNAseq, NTA, flow cytometry, and IHC staining. Compared with tumor tissues which represent only one part of the whole tumor, liquid biopsies contain more homogeneous molecules from the blood circulation to minimize bias in the detection of biomarkers. In contrast to an in-treatment time point, the detection of biomarkers at a pre-treatment time point may allow more time for therapeutic decision making to improve patient outcomes. In addition, the accuracy and reproducibility of the findings of current biomarkers should be taken into consideration in terms of the sample size, patient heterogeneity, methodological difference, and study design. The prognostic value of some biomarkers (such as AFP, IL-6, NLR, CTC, and PNI) in HCC patients receiving atezolizumab plus bevacizumab combination therapy has been evaluated in different lines of studies. The association of these biomarkers with patient outcomes is consistent among different studies, supporting their potential in clinical use. However, the threshold of the same biomarker, even detected using the same method at the same time point, varied among different studies. Aside from these biomarkers, the prognostic significance of many other single or combination of biomarker(s) remains only validated in one study each. Therefore, more studies are still needed to reach a consensus on the outcome correlation and prognostic threshold for the current biomarkers to facilitate their translation into clinical application. Moreover, a prospective multicenter large cohort study with a stratified analysis of patient characteristics is required to provide more robust and unbiased evidence. The establishment of standardized methodological and technical protocols for biomarker measurement in different types of specimens is necessary to improve the consistency and reliability of the biomarkers. Future investigation is worthwhile to develop biomarker panels that are tailored for specific characteristics of patients through the facilitation of artificial intelligence-based approaches in combination with current bioinformatics software. In addition to atezolizumab plus bevacizumab combination therapy, durvalumab (an anti-PD-L1 antibody) in combination with tremelimumab (an anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) antibody) is the other preferred FDA-approved first-line systemic therapy for the treatment of patients with unresectable HCC.52,53 However, current studies regarding the prognostic biomarkers for HCC patients treated with durvalumab plus tremelimumab combination therapy remain very limited, raising an urgent need for discovering biomarkers for this therapy. This is also the reason why the present review focuses on the biomarkers for atezolizumab plus bevacizumab combination therapy. Furthermore, the therapeutic efficacy of three-drug combinations using an atezolizumab plus bevacizumab framework for unresectable HCC in the first-line setting is being evaluated in several clinical trials, including a phase II trial for atezolizumab plus bevacizumab plus SRF388 (an anti-interleukin 27 antibody), 54 a phase II/III trial for atezolizumab plus bevacizumab plus ipilimumab (an anti-CTLA-4 antibody), 55 and a phase III trial for atezolizumab plus bevacizumab plus tiragolumab (an anti-T-cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) antibody). 56 Compared with atezolizumab plus bevacizumab, the triplet combination of atezolizumab, bevacizumab, and tiragolumab has shown a longer median OS (28.9 months vs 15.1 months) and RFS (12.3 months vs 4.2 months), as well as a higher ORR (43% vs 11%) in a phase Ib/II trial for unresectable HCC. 57 The current biomarkers for atezolizumab plus bevacizumab combination therapy may have promising potential to guide the development of biomarkers for tiragolumab in combination with atezolizumab plus bevacizumab in patients with unresectable HCC in the future.
Footnotes
Acknowledgements
This work was supported by grants from the China Medical University Hospital, Taichung, Taiwan (DMR-113-027).
Author Contributions
Conceptualization, Long-Bin Jeng, Horng-Ren Yang, and Chiao-Fang Teng; Funding acquisition, Chiao-Fang Teng; Visualization, Long-Bin Jeng, Horng-Ren Yang, and Chiao-Fang Teng; Writing—original draft, Chiao-Fang Teng; Writing—review and editing, Chiao-Fang Teng.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by grants from the China Medical University Hospital, Taichung, Taiwan (DMR-113-027).
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
