The prognostic role of immune checkpoint markers programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) in a large, multicenter prostate cancer cohort

Pembrolizumab for metastatic castration-resistant prostate cancer: trials and tribulations

INTRODUCTION

Immunotherapies have revolutionized the management of various malignancies but have only recently been evaluated systematically in prostate cancer. Pembrolizumab, a programmed-death 1 (PD-1) blocking antibody, has been utilized in a small subset of prostate cancer patients with mismatch repair deficiency/microsatellite instability, but has now been assessed in broader populations of metastatic prostate cancer patients.

AREAS COVERED

The results of four pembrolizumab-based phase III clinical trials for metastatic castration-resistant prostate cancer (mCRPC) and metastatic hormone-sensitive prostate cancer (mHSPC) patients, including KEYNOTE-641, KEYNOTE-921, KEYNOTE-991, and KEYLYNK-010 are summarized. Programmed death-ligand 1 (PD-L1) expression, the efficacy of pembrolizumab in prostate cancer patients with certain molecular defects, and emerging pembrolizumab-based therapeutic combinations are also reviewed.

EXPERT OPINION

Pembrolizumab has not benefitted unselected metastatic prostate cancer patients when combined with chemotherapy, next-generation hormonal agents (NHA), or poly(ADP-ribose) polymerase inhibitors (PARPi). PD-L1 positivity does not predict the response to pembrolizumab in this disease. A small number of responding patients can likely be explained by rare genetic and molecular defects, and more innovative combination strategies are needed to improve outcomes in prostate cancer patients who are not sensitive to pembrolizumab. Emphasis should be placed on developing additional or alternative immuno-oncology approaches beyond classical immune checkpoint inhibition.

Comprehensive Analysis of DNA Methyltransferases Expression in Primary and Relapsed Ovarian Carcinoma

BACKGROUND

Despite recent advances in epithelial ovarian carcinoma (EOC) treatment, its recurrence and mortality rates have not improved significantly. DNA hypermethylation has generally been associated with an ominous prognosis and chemotherapy resistance, but the role of DNA methyltransferases (DNMTs) in EOC remains to be investigated.

METHODS

In the current study, we systematically retrieved gene expression data from patients with EOC and studied the immunohistochemical expression of DNMTs in 108 primary and 26 relapsed tumors.

RESULTS

Our results showed that the DNMT1, DNMT3A, DNMT3B and DNMT3L RNA levels were higher and the DNMT2 level was lower in tumors compared to non-neoplastic tissue, and DNMT3A and DNMT2 expression decreased from Stage-II to Stage-IV carcinomas. The proteomic data also suggested that the DNMT1 and DNMT3A levels were increased in the tumors. Similarly, the DNMT1, DNMT3A and DNMT3L protein levels were overexpressed and DNMT2 expression was reduced in high-grade carcinomas compared to non-neoplastic tissue and low-grade tumors. Moreover, DNMT1 and DNMT3L were increased in relapsed tumors compared to their primaries. The DNMT3A, DNMT1 and DNMT3B mRNA levels were correlated with overall survival.

CONCLUSIONS

Our study demonstrates that DNMT1 and DNMT3L are upregulated in primary high-grade EOC and further increase in relapses, whereas DNMT3A is upregulated only in the earlier stages of cancer progression. DNMT2 downregulation highlights the presumed tumor-suppressor activity of this gene in ovarian carcinoma.

Genomic and Phenotypic Biomarkers for Precision Medicine Guidance in Advanced Prostate Cancer

OPINION STATEMENT

Prostate cancer (PCa) is the second most diagnosed malignant neoplasm and is one of the leading causes of cancer-related death in men worldwide. Despite significant advances in screening and treatment of PCa, given the heterogeneity of this disease, optimal personalized therapeutic strategies remain limited. However, emerging predictive and prognostic biomarkers based on individual patient profiles in combination with computer-assisted diagnostics have the potential to guide precision medicine, where patients may benefit from therapeutic approaches optimally suited to their disease. Also, the integration of genotypic and phenotypic diagnostic methods is supporting better informed treatment decisions. Focusing on advanced PCa, this review discusses polygenic risk scores for screening of PCa and common genomic aberrations in androgen receptor (AR), PTEN-PI3K-AKT, and DNA damage response (DDR) pathways, considering clinical implications for diagnosis, prognosis, and treatment prediction. Furthermore, we evaluate liquid biopsy, protein biomarkers such as serum testosterone levels, SLFN11 expression, total alkaline phosphatase (tALP), neutrophil-to-lymphocyte ratio (NLR), tissue biopsy, and advanced imaging tools, summarizing current phenotypic biomarkers and envisaging more effective utilization of diagnostic and prognostic biomarkers in advanced PCa. We conclude that prognostic and treatment predictive biomarker discovery can improve the management of patients, especially in metastatic stages of advanced PCa. This will result in decreased mortality and enhanced quality of life and help design a personalized treatment regimen.

DNA Damage Repair Pathways in Prostate Cancer: A Narrative Review of Molecular Mechanisms, Emerging Biomarkers and Therapeutic Targets in Precision Oncology

Prostate cancer (PCa) has a distinct molecular signature, including characteristic chromosomal translocations, gene deletions and defective DNA damage repair mechanisms. One crucial pathway involved is homologous recombination deficiency (HRD) and it is found in almost 20% of metastatic castrate-resistant PCa (mCRPC). Inherited/germline mutations are associated with a hereditary predisposition to early PCa development and aggressive behavior. BRCA2, ATM and CHECK2 are the most frequently HRD-mutated genes. BRCA2-mutated tumors have unfavorable clinical and pathological characteristics, such as intraductal carcinoma. PARP inhibitors, due to the induction of synthetic lethality, have been therapeutically approved for mCRPC with HRD alterations. Mutations are detected in metastatic tissue, while a liquid biopsy is utilized during follow-up, recognizing acquired resistance mechanisms. The mismatch repair (MMR) pathway is another DNA repair mechanism implicated in carcinogenesis, although only 5% of metastatic PCa is affected. It is associated with aggressive disease. PD-1 inhibitors have been used in MMR-deficient tumors; thus, the MMR status should be tested in all metastatic PCa cases. A surrogate marker of defective DNA repair mechanisms is the tumor mutational burden. PDL-1 expression and intratumoral lymphocytes have ambivalent predictive value. Few experimental molecules have been so far proposed as potential biomarkers. Future research may further elucidate the role of DNA damage pathways in PCa, revealing new therapeutic targets and predictive biomarkers.

Immunotherapy in Prostate Cancer: State of Art and New Therapeutic Perspectives

Prostate cancer (PC) is the most common type of tumor in men. In the early stage of the disease, it is sensitive to androgen deprivation therapy. In patients with metastatic castration-sensitive prostate cancer (mHSPC), chemotherapy and second-generation androgen receptor therapy have led to increased survival. However, despite advances in the management of mHSPC, castration resistance is unavoidable and many patients develop metastatic castration-resistant disease (mCRPC). In the past few decades, immunotherapy has dramatically changed the oncology landscape and has increased the survival rate of many types of cancer. However, immunotherapy in prostate cancer has not yet given the revolutionary results it has in other types of tumors. Research into new treatments is very important for patients with mCRPC because of its poor prognosis. In this review, we focus on the reasons for the apparent intrinsic resistance of prostate cancer to immunotherapy, the possibilities for overcoming this resistance, and the clinical evidence and new therapeutic perspectives regarding immunotherapy in prostate cancer with a look toward the future.

PD-L1 expression and CD8 positive lymphocytes in human neoplasms: A tissue microarray study on 11,838 tumor samples

BACKGROUND

Programmed death ligand 1 (PD-L1) is the target of immune checkpoint inhibitor therapies in a growing number of tumor types, but a unanimous picture on PD-L1 expression across cancer types is lacking.

MATERIALS AND METHODS

We analyzed immunohistochemical PD-L1 expression in 11,838 samples from 118 human tumor types and its relationship with tumor infiltrating CD8 positive lymphocytes.

RESULTS

At a cut-off level of 10% positive tumor cells, PD-L1 positivity was seen in 85 of 118 (72%) tumor types, including thymoma (100% positive), Hodgkin's lymphoma (93%), anaplastic thyroid carcinoma (76%), Kaposi sarcoma (71%), sarcomatoid urothelial carcinoma (71%), and squamous cell carcinoma of the penis (67%), cervix (65%), floor of the mouth (61%), the lung (53%), and pharynx (50%). In immune cells, PD-L1 positivity was detectable in 103 (87%) tumor types, including tumors of haematopoetic and lymphoid tissues (75% to 100%), Warthin tumors of the parotid glands (95%) and Merkel cell carcinoma (82%). PD-L1 positivity in tumor cells was significantly correlated with the number of intratumoral CD8 positive lymphocytes across all tumor types as well as in individual tumor types, including serous carcinoma of the ovary, invasive breast carcinoma of no special type, intestinal gastric adenocarcinoma, and liposarcoma (p< 0.0001 each).

CONCLUSIONS

PD-L1 expression in tumor and inflammatory cells is found in a wide range of human tumor types. Higher rates of tumor infiltrating CD8 positive lymphocytes in PD-L1 positive than in PD-L1 negative cancers suggest that the antitumor immune response may trigger tumoral PD-L1 expression.

The role of PD-1/PD-L1 and application of immune-checkpoint inhibitors in human cancers

Programmed cell death protein-1 (PD-1) is a checkpoint receptor expressed on the surface of various immune cells. PD-L1, the natural receptor for PD-1, is mainly expressed in tumor cells. Studies have indicated that PD-1 and PD-L1 are closely associated with the progression of human cancers and are promising biomarkers for cancer therapy. Moreover, the interaction of PD-1 and PD-L1 is one of the important mechanism by which human tumors generate immune escape. This article provides a review on the role of PD-L1/PD-1, mechanisms of immune response and resistance, as well as immune-related adverse events in the treatment of anti-PD-1/PD-L1 immunotherapy in human cancers. Moreover, we summarized a large number of clinical trials to successfully reveal that PD-1/PD-L1 Immune-checkpoint inhibitors have manifested promising therapeutic effects, which have been evaluated from different perspectives, including overall survival, objective effective rate and medium progression-free survival. Finally, we pointed out the current problems faced by PD-1/PD-L1 Immune-checkpoint inhibitors and its future prospects. Although PD-1/PD-L1 immune checkpoint inhibitors have been widely used in the treatment of human cancers, tough challenges still remain. Combination therapy and predictive models based on integrated biomarker determination theory may be the future directions for the application of PD-1/PD-L1 Immune-checkpoint inhibitors in treating human cancers.

The Cellular and Molecular Immunotherapy in Prostate Cancer

In recent history, immunotherapy has become a viable cancer therapeutic option. However, over many years, its tenets have changed, and it now comprises a range of cancer-focused immunotherapies. Clinical trials are currently looking into monotherapies or combinations of medicines that include immune checkpoint inhibitors (ICI), CART cells, DNA vaccines targeting viruses, and adoptive cellular therapy. According to ongoing studies, the discipline should progress by incorporating patient-tailored immunotherapy, immune checkpoint blockers, other immunotherapeutic medications, hormone therapy, radiotherapy, and chemotherapy. Despite significantly increasing morbidity, immunotherapy can intensify the therapeutic effect and enhance immune responses. The findings for the immunotherapy treatment of advanced prostate cancer (PCa) are compiled in this study, showing that is possible to investigate the current state of immunotherapy, covering new findings, PCa treatment techniques, and research perspectives in the field’s unceasing evolution.

Prostate cancer immunotherapy: a review of recent advancements with novel treatment methods and efficacy

Immunotherapy remains to be an appealing treatment option for prostate cancer with some documented promise. Prostate cancer is traditionally considered as an immunologically "cold" tumor with low tumor mutation burden, low expression of PD-L1, sparse T-cell infiltration, and a immunosuppressive tumor microenvironment (TME). Sipuleucel-T (Provenge) is the first FDA approved immunotherapeutic agent for the treatment of asymptomatic or minimally symptomatic metastatic castrate resistant prostate cancer (mCRPC); demonstrating a benefit in overall survival. However various clinical trials by immune checkpoint inhibitors (ICIs) and their combinations with other drugs have shown limited responses in mCRPC. Up to now, only a small subset of patients with mismatch repair deficiency/microsatellite instability high and CDK12 mutations can clinically benefit from ICIs and/or their combinations with other agents, such as DNA damage agents. The existence of a large heterogeneity in genomic alterations and a complex TME in prostate cancer suggests the need for identifying new immunotherapeutic targets. As well as designing personalized immunotherapy strategies based on patient-specific molecular signatures. There is also a need to adjust strategies to overcome histologic barriers such as tissue hypoxia and dense stroma. The racial differences of immunological responses between men of diverse ethnicities also merit further investigation to improve the efficacy of immunotherapy and better patient selection in prostate cancer.

The association between PI3K, JAK/STAT pathways with the PDL-1 expression in prostate cancer

Programmed cell death protein-1/programmed death-ligand-1 (PD-1/PDL-1) signalling pathway has gained attention in prostate cancer. The relationship between pSTAT-1, pSTAT-3 expressions and PTEN loss with PDL-1 expression was assessed and the effects of the pathways on prostate cancer prognosis were evaluated. Patients who underwent radical prostatectomy between 2011 and 2017 were included in our study. Prostatectomy materials were evaluated using immunohistochemical staining of pSTAT-1, pSTAT-3, PTEN, and PDL-1. The relationship between PDL-1 and pSTAT-1, pSTAT-3 expressions and PTEN loss was evaluated. Additionally, factors affecting biochemical recurrence-free survival and clinical progression-free survival were analysed. Within100 patients, 9 of 11 patients with PDL-1 expression also had intermediate-high pSTAT-1 staining intensity, and those with PDL-1 expression had higher pSTAT-1 staining intensity than those without (81.9% vs. 56.2%, p = 0.014). In univariate analysis, pSTAT-1, pSTAT-3 and PDL-1 expressions had significant impact on biochemical recurrence-free and clinical progression-free survival. In multivariate analysis, pSTAT-1 staining intensity with radical prostatectomy ISUP grade in terms of biochemical recurrence-free survival and the pSTAT-1 H-score with radical prostatectomy ISUP grade in terms of clinical progression-free survival were independent risk factors. Moderate-high expression of pSTAT-1 was closely associated with PDL-1 expression, and pSTAT-1 was also a predictor of biochemical recurrence and clinical progression.

Traditional Chinese medicine CFF-1 exerts a potent anti-tumor immunity to hinder tumor growth and metastasis in prostate cancer through EGFR/JAK1/STAT3 pathway to inhibit PD-1/PD-L1 checkpoint signaling

BACKGROUND

Traditional Chinese Medicine (TCM) CFF-1 has been used in clinic for prostate cancer therapy in China. We reported before CFF-1 induced cell apoptosis via suppressing EGFR-related pathways, reminding us its potential role associated with antitumor immunity.

PURPOSE

The study was aimed to investigate the regulatory mechanism of CFF-1 on PD-L1/PD-1-mediated tumor immune escape.

METHODS

Prostate-specific antigen (PSA) test and the functional assessment of cancer therapy-prostate (FACT-P) and karnosky performance status (KPS) questionnaires were carried out to evaluate patient' condition before and after therapy. Flow cytometry (FCM) was used for analyzing cell apoptosis, T lymphocyte subsets and cell cycle. Western blotting and Immunohistochemistry (IHC) were performed to measure protein expressions. The synergy of drug combination was assessed by calculating combination index (CI).

RESULTS

CFF-1 obviously decreased PSA and improved the quality of life in patients with advanced prostate cancer. PD-L1 was highly expressed in prostate cancer cells including LNCaP, 22Rv1, PC-3, DU145 and RM-1. PD-1/PD-L1 was upregulated in tumorigenesis and tumor progression of subcutaneous homograft mouse model with immune response, where CD3+ T cell subsets were declined. CFF-1 inhibited PD-L1 expression in prostate cancer cells in a time/dose-dependent manner and blocked tumor growth by suppressing PD-1/PD-L1 upregulation to promote the recovery of CD3+ T lymphocytes, especially CD4+ T cell subset, accompanied by the downregulation of CD4+ FOXP3+ T cell subset. CFF-1 also prolonged the survival and inhibited lung metastasis in tail vein prostate cancer mouse model while repressing PD-1/PD-L1. CFF-1 in combination with docetaxol (DTX) produced a synergistic effects by sensitizing the inhibitory effect of DTX on JAK1/STAT3 pathway targeting PD-L1 blockade.

CONCLUSION

CFF-1 inhibited tumor growth and lung metastasis by blocking PD-1/PD-L1 to ameliorate T lymphocyte immune response through EGFR/JAK1/STAT3 pathway, suggesting that CFF-1 might be a promising treatment to resist tumor immunosuppression for prostate cancer patients.

Characterization of a Pyroptosis-Related Signature for Prognosis Prediction and Immune Microenvironment Infiltration in Prostate Cancer

This study was aimed at constructing a pyroptosis-related signature for prostate cancer (PCa) and elucidating the prognosis and immune landscape and the sensitivity of immune checkpoint blockade (ICB) therapy in signature-define subgroups of PCa. We identified 22 differentially expressed pyroptosis-related genes in PCa from The Cancer Genome Atlas (TCGA) database. The pyroptosis-related genes could divide PCa patients into two clusters with differences in survival. Seven genes were determined to construct a signature that was confirmed by qRT-PCR to be closely associated with the biological characteristics of malignant PCa. The signature could effectively and independently predict the biochemical recurrence (BCR) of PCa, which was validated in the GSE116918 and GSE21034. We found that patients in the high-risk group were more prone to BCR and closely associated with high-grade and advanced-stage disease progression. Outperforming clinical characteristics and nine published articles, our signature demonstrated excellent predictive performance. The patients in the low-risk group were strongly related to the high infiltration of various immune cells including CD8+ T cells and plasma B cells. Furthermore, the high-risk group with higher TMB levels and expression of immune checkpoints was more likely to benefit from immune checkpoint therapy such as PD-1 and CTLA-4 inhibitors. The sensitivity to chemotherapy, endocrine, and targeted therapy showed significant differences in the two risk groups. Our signature was a novel therapeutic strategy to distinguish the prognosis and guide treatment strategies.

Immunotherapy in Advanced Prostate Cancer-Light at the End of the Tunnel?

Immunotherapeutic treatment approaches are now an integral part of the treatment of many solid tumors. However, attempts to integrate immunotherapy into the treatment of prostate cancer have been disappointing so far. This is due to a highly immunosuppressive, “cold” tumor microenvironment, which is characterized, for example, by the absence of cytotoxic T cells, an increased number of myeloid-derived suppressor cells or regulatory T cells, a decreased number of tumor antigens, or a defect in antigen presentation. The consequence is a reduced efficacy of many established immunotherapeutic treatments such as checkpoint inhibitors. However, a growing understanding of the underlying mechanisms of tumor–immune system interactions raises hopes that immunotherapeutic strategies can be optimized in the future. The aim of this review is to provide an overview of the current status and future directions of immunotherapy development in prostate cancer. Background information on immune response and tumor microenvironment will help to better understand current therapeutic strategies under preclinical and clinical development.

Prognostic Value of Programmed Death Ligand-1 Expression in Solid Tumors Irrespective of Immunotherapy Exposure: A Systematic Review and Meta-Analysis

BACKGROUND

The programmed cell death-1/programmed cell death ligand-1 (PD-L1) pathway, which plays a crucial role in cancer immune surveillance, is the target of several approved immunotherapeutic agents and is used as a predictive biomarker in some solid tumors. However, its use as a prognostic marker (i.e., regardless of therapy used) is not established clearly with available data demonstrating inconsistent prognostic impact of PD-L1 expression in solid tumors.

METHODS

We conducted a systematic literature search of electronic databases and identified publications exploring the effect of PD-L1 expression on overall survival and/or disease-free survival. Hazard ratios were pooled in a meta-analysis using generic inverse-variance and random-effects modeling. We used the Deeks method to explore subgroup differences based on disease site, stage of disease, and method of PD-L1 quantification.

RESULTS

One hundred and eighty-six studies met the inclusion criteria. Programmed cell death ligand-1 expression was associated with worse overall survival (hazard ratio 1.33, 95% confidence interval 1.26-1.39; p < 0.001). There was significant heterogeneity between disease sites (subgroup p = 0.002) with pancreatic, hepatocellular, and genitourinary cancers associated with the highest magnitude of adverse outcomes. Programmed cell death ligand-1 was also associated with worse overall disease-free survival (hazard ratio 1.19, 95% confidence interval 1.09-1.30; p < 0.001). Stage of disease did not significantly affect the results (subgroup p = 0.52), nor did the method of quantification via immunohistochemistry or messenger RNA (subgroup p = 0.70).

CONCLUSIONS

High expression of PD-L1 is associated with worse survival in solid tumors albeit with significant heterogeneity among tumor types. The effect is consistent in early-stage and metastatic disease and is not sensitive to method of PD-L1 quantification. These data can provide additional information for the counseling of patients with cancer about prognosis.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review (Part 6): Correlation of PD-L1 Expression with the Status of Mismatch Repair System, BRCA, PTEN, and Other Genes

Pembrolizumab (anti-PD-1) is allowed in selected metastatic castration-resistant prostate cancer (PC) patients showing microsatellite instability/mismatch repair system deficiency (MSI-H/dMMR). BRCA1/2 loss-of-function is linked to hereditary PCs and homologous recombination DNA-repair system deficiency: poly-ADP-ribose-polymerase inhibitors can be administered to BRCA-mutated PC patients. Recently, docetaxel-refractory metastatic castration-resistant PC patients with BRCA1/2 or ATM somatic mutations had higher response rates to pembrolizumab. PTEN regulates cell cycle/proliferation/apoptosis through pathways including the AKT/mTOR, which upregulates PD-L1 expression in PC. Our systematic literature review (PRISMA guidelines) investigated the potential correlations between PD-L1 and MMR/MSI/BRCA/PTEN statuses in PC, discussing few other relevant genes. Excluding selection biases, 74/677 (11%) PCs showed dMMR/MSI; 8/67 (12%) of dMMR/MSI cases were PD-L1+. dMMR-PCs included ductal (3%) and acinar (14%) PCs (all cases tested for MSI were acinar-PCs). In total, 15/39 (39%) PCs harbored BRCA1/2 aberrations: limited data are available for PD-L1 expression in these patients. 13/137 (10%) PTEN- PCs were PD-L1+; 10/29 (35%) PD-L1+ PCs showed PTEN negativity. SPOP mutations may increase PD-L1 levels, while the potential correlation between PD-L1 and ERG expression in PC should be clarified. Further research should verify how the efficacy of PD-1 inhibitors in metastatic castration-resistant PCs is related to dMMR/MSI, DNA-damage repair genes defects, or PD-L1 expression.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 7: PD-L1 Expression in Liquid Biopsy

Liquid biopsy is an accessible, non-invasive diagnostic tool for advanced prostate cancer (PC) patients, potentially representing a real-time monitoring test for tumor evolution and response to treatment through the analysis of circulating tumor cells (CTCs) and exosomes. We performed a systematic literature review (PRISMA guidelines) to describe the current knowledge about PD-L1 expression in liquid biopsies of PC patients: 101/159 (64%) cases revealed a variable number of PD-L1+ CTCs. Outcome correlations should be investigated in larger series. Nuclear PD-L1 expression by CTCs was occasionally associated with worse prognosis. Treatment (abiraterone, enzalutamide, radiotherapy, checkpoint-inhibitors) influenced PD-L1+ CTC levels. Discordance in PD-L1 status was detected between primary vs. metastatic PC tissue biopsies and CTCs vs. corresponding tumor tissues. PD-L1 is also released by PC cells through soluble exosomes, which could inhibit the T cell function, causing immune evasion. PD-L1+ PC-CTC monitoring and genomic profiling may better characterize the ongoing aggressive PC forms compared to PD-L1 evaluation on primary tumor biopsies/prostatectomy specimens (sometimes sampled a long time before recurrence/progression). Myeloid-derived suppressor cells and dendritic cells (DCs), which may have immune-suppressive effects in tumor microenvironment, have been found in PC patients circulation, sometimes expressing PD-L1. Occasionally, their levels correlated to clinical outcome. Enzalutamide-progressing castration-resistant PC patients revealed increased PD-1+ T cells and circulating PD-L1/2+ DCs.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 5: Epigenetic Regulation of PD-L1

Epigenetic alterations (including DNA methylation or miRNAs) influence oncogene/oncosuppressor gene expression without changing the DNA sequence. Prostate cancer (PC) displays a complex genetic and epigenetic regulation of cell-growth pathways and tumor progression. We performed a systematic literature review (following PRISMA guidelines) focused on the epigenetic regulation of PD-L1 expression in PC. In PC cell lines, CpG island methylation of the CD274 promoter negatively regulated PD-L1 expression. Histone modifiers also influence the PD-L1 transcription rate: the deletion or silencing of the histone modifiers MLL3/MML1 can positively regulate PD-L1 expression. Epigenetic drugs (EDs) may be promising in reprogramming tumor cells, reversing epigenetic modifications, and cancer immune evasion. EDs promoting a chromatin-inactive transcriptional state (such as bromodomain or p300/CBP inhibitors) downregulated PD-L1, while EDs favoring a chromatin-active state (i.e., histone deacetylase inhibitors) increased PD-L1 expression. miRNAs can regulate PD-L1 at a post-transcriptional level. miR-195/miR-16 were negatively associated with PD-L1 expression and positively correlated to longer biochemical recurrence-free survival; they also enhanced the radiotherapy efficacy in PC cell lines. miR-197 and miR-200a-c positively correlated to PD-L1 mRNA levels and inversely correlated to the methylation of PD-L1 promoter in a large series. miR-570, miR-34a and miR-513 may also be involved in epigenetic regulation.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 3: PD-L1, Intracellular Signaling Pathways and Tumor Microenvironment

The tumor microenvironment (TME) includes immune (T, B, NK, dendritic), stromal, mesenchymal, endothelial, adipocytic cells, extracellular matrix, and cytokines/chemokines/soluble factors regulating various intracellular signaling pathways (ISP) in tumor cells. TME influences the survival/progression of prostate cancer (PC), enabling tumor cell immune-evasion also through the activation of the PD-1/PD-L1 axis. We have performed a systematic literature review according to the PRISMA guidelines, to investigate how the PD-1/PD-L1 pathway is influenced by TME and ISPs. Tumor immune-escape mechanisms include suppression/exhaustion of tumor infiltrating cytotoxic T lymphocytes, inhibition of tumor suppressive NK cells, increase in immune-suppressive immune cells (regulatory T, M2 macrophagic, myeloid-derived suppressor, dendritic, stromal, and adipocytic cells). IFN-γ (the most investigated factor), TGF-β, TNF-α, IL-6, IL-17, IL-15, IL-27, complement factor C5a, and other soluble molecules secreted by TME components (and sometimes increased in patients' serum), as well as and hypoxia, influenced the regulation of PD-L1. Experimental studies using human and mouse PC cell lines (derived from either androgen-sensitive or androgen-resistant tumors) revealed that the intracellular ERK/MEK, Akt-mTOR, NF-kB, WNT and JAK/STAT pathways were involved in PD-L1 upregulation in PC. Blocking the PD-1/PD-L1 signaling by using immunotherapy drugs can prevent tumor immune-escape, increasing the anti-tumor activity of immune cells.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 1: Focus on Immunohistochemical Results with Discussion of Pre-Analytical and Interpretation Variables

Immunotherapy targeting the PD-1-PD-L1 axis yielded good results in treating different immunologically ''hot'' tumors. A phase II study revealed good therapeutic activity of pembrolizumab in selected prostatic carcinoma (PC)-patients. We performed a systematic literature review (PRISMA guidelines), which analyzes the immunohistochemical expression of PD-L1 in human PC samples and highlights the pre-analytical and interpretation variables. Interestingly, 29% acinar PCs, 7% ductal PCs, and 46% neuroendocrine carcinomas/tumors were PD-L1+ on immunohistochemistry. Different scoring methods or cut-off criteria were applied on variable specimen-types, evaluating tumors showing different clinic-pathologic features. The positivity rate of different PD-L1 antibody clones in tumor cells ranged from 3% (SP142) to 50% (ABM4E54), excluding the single case tested for RM-320. The most tested clone was E1L3N, followed by 22C3 (most used for pembrolizumab eligibility), SP263, SP142, and 28-8, which gave the positivity rates of 35%, 11-41% (depending on different scoring systems), 6%, 3%, and 15%, respectively. Other clones were tested in <200 cases. The PD-L1 positivity rate was usually higher in tumors than benign tissues. It was higher in non-tissue microarray specimens (41-50% vs. 15%), as PC cells frequently showed heterogenous or focal PD-L1-staining. PD-L1 was expressed by immune or stromal cells in 12% and 69% cases, respectively. Tumor heterogeneity, inter-institutional preanalytics, and inter-observer interpretation variability may account for result biases.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 4: Experimental Treatments in Pre-Clinical Studies (Cell Lines and Mouse Models)

In prostate cancer (PC), the PD-1/PD-L1 axis regulates various signaling pathways and it is influenced by extracellular factors. Pre-clinical experimental studies investigating the effects of various treatments (alone or combined) may discover how to overcome the immunotherapy-resistance in PC-patients. We performed a systematic literature review (PRISMA guidelines) to delineate the landscape of pre-clinical studies (including cell lines and mouse models) that tested treatments with effects on PD-L1 signaling in PC. NF-kB, MEK, JAK, or STAT inhibitors on human/mouse, primary/metastatic PC-cell lines variably down-modulated PD-L1-expression, reducing chemoresistance and tumor cell migration. If PC-cells were co-cultured with NK, CD8+ T-cells or CAR-T cells, the immune cell cytotoxicity increased when PD-L1 was downregulated (opposite effects for PD-L1 upregulation). In mouse models, radiotherapy, CDK4/6-inhibitors, and RB deletion induced PD-L1-upregulation, causing PC-immune-evasion. Epigenetic drugs may reduce PD-L1 expression. In some PC experimental models, blocking only the PD-1/PD-L1 pathway had limited efficacy in reducing the tumor growth. Anti-tumor effects could be increased by combining the PD-1/PD-L1 blockade with other approaches (inhibitors of tyrosine kinase, PI3K/mTOR or JAK/STAT3 pathways, p300/CBP; anti-RANKL and/or anti-CTLA-4 antibodies; cytokines; nitroxoline; DNA/cell vaccines; radiotherapy/Radium-223).

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 2: Clinic-Pathologic Correlations

Many studies have investigated the potential prognostic and predictive role of PD-L1 in prostatic carcinoma (PC). We performed a systematic literature review (PRISMA guidelines) to critically evaluate human tissue-based studies (immunohistochemistry, molecular analysis, etc.), experimental research (cell lines, mouse models), and clinical trials. Despite some controversial results and study limitations, PD-L1 expression by tumor cells may be related to clinic-pathologic features of adverse outcome, including advanced tumor stage (high pT, presence of lymph node, and distant metastases), positivity of surgical margins, high Grade Group, and castration resistance. Different PD-L1 positivity rates may be observed in matched primary PCs and various metastatic sites of the same patients. Over-fixation, type/duration of decalcification, and PD-L1 antibody clone may influence the immunohistochemical analysis of PD-L1 on bone metastases. PD-L1 seemed expressed more frequently by castration-resistant PCs (49%) as compared to hormone-sensitive PCs (17%). Some series found that PD-L1 positivity was associated with decreased time to castration resistance. Treatment with ipilimumab, cyclophosphamide/GVAX/degarelix, or degarelix alone may increase PD-L1 expression. Correlation of PD-L1 positivity with overall survival and outcomes related to tumor recurrence were rarely investigated; the few analyzed series produced conflicting results and sometimes showed limitations. Further studies are required. The testing and scoring of PD-L1 should be standardized.

Immune checkpoint B7-H3 protein expression is associated with poor outcome and androgen receptor status in prostate cancer

BACKGROUND

Novel immune checkpoint-based immunotherapies may benefit specific groups of prostate cancer patients who are resistant to other treatments.

METHODS

We analyzed by immunohistochemistry the expression of B7-H3, PD-L1/B7-H1, and androgen receptor (AR) in tissue samples from 120 prostate adenocarcinoma patients treated with radical prostatectomy in Spain, and from 206 prostate adenocarcinoma patients treated with radical prostatectomy in Norway.

RESULTS

B7-H3 expression correlated positively with AR expression and was associated with biochemical recurrence in the Spanish cohort, but PD-L1 expression correlated with neither of them. Findings for B7-H3 were validated in the Norwegian cohort, where B7-H3 expression correlated positively with Gleason grade, surgical margins, seminal vesicle invasion, and CAPRA-S risk group, and was associated with clinical recurrence. High B7-H3 expression in the Norwegian cohort was also consistent with positive AR expression.

CONCLUSION

These results suggest distinct clinical relevance of the two immune checkpoint proteins PD-L1 and B7-H3 in prostate cancer. Our findings highlight B7-H3 as an actionable novel immune checkpoint protein in prostate cancer.

Glyoxalase-1-Dependent Methylglyoxal Depletion Sustains PD-L1 Expression in Metastatic Prostate Cancer Cells: A Novel Mechanism in Cancer Immunosurveillance Escape and a Potential Novel Target to Overcome PD-L1 Blockade Resistance

Simple Summary

Metastatic prostate cancer (mPCa) is a well-known lethal condition. One of the mechanisms through which PCa cells become so aggressive is the avoidance of immune surveillance that further fosters cell growth, invasion, and migration. PD-L1/PD-1 axis plays a crucial role in inhibiting cytotoxic T cells and maintaining an immunosuppressive cancer microenvironment. Hence, targeting PD-L1/PD-1 axis represents a potential way to control mPCa. Unfortunately, mPCa patients do not respond to PD-L1/PD-1 axis blockade, focusing the research to understand the possible underpinning mechanisms. Our results provide a novel pathway taking part in cancer immunosurveillance escape and in the above-mentioned immunotherapy resistance, which provides the basis for additional studies aimed at developing novel therapeutic opportunities, possibly also in combination with antibodies blocking PD-L1/PD-1 axis.

Abstract

Metastatic prostate cancer (mPCa) is a disease for which to date there is not curative therapy. Even the recent and attractive immunotherapeutic approaches targeting PD-L1, an immune checkpoint protein which helps cancer cells to escape from immunosurveillance, have proved ineffective. A better understanding of the molecular mechanisms contributing to keep an immunosuppressive microenvironment associated with tumor progression and refractoriness to PD-L1 inhibitors is urgently needed. In the present study, by using gene silencing and specific activators or scavengers, we demonstrated, in mPCa cell models, that methylglyoxal (MG), a potent precursor of advanced glycation end products (AGEs), especially 5-hydro-5-methylimidazolone (MG-H1), and its metabolizing enzyme, glyoxalase 1 (Glo1), contribute to maintain an immunosuppressive microenvironment through MG-H1-mediated PD-L1 up-regulation and to promote cancer progression. Moreover, our findings suggest that this novel mechanism might be responsible, at least in part, of mPCa resistance to PD-L1 inhibitors, such as atezolizumab, and that targeting it may sensitize cells to this PD-L1 inhibitor. These findings provide novel insights into the mechanisms of mPCa immunosurveillance escape and help in providing the basis to foster in vivo research toward novel therapeutic strategies for immunotherapy of mPCa.

Immune Inflammation Pathways as Therapeutic Targets to Reduce Lethal Prostate Cancer in African American Men

Despite substantial improvements in cancer survival, not all population groups have benefitted equally from this progress. For prostate cancer, men of African descent in the United States and England continue to have about double the rate of fatal disease compared to other men. Studies suggest that when there is equal access to care, survival disparities are greatly diminished. However, notable differences exist in prostate tumor biology across population groups. Ancestral factors and disparate exposures can lead to altered tumor biology, resulting in a distinct disease etiology by population group. While equal care remains the key target to improve survival, additional efforts should be made to gain comprehensive knowledge of the tumor biology in prostate cancer patients of African descent. Such an approach may identify novel intervention strategies in the era of precision medicine. A growing body of evidence shows that inflammation and the immune response may play a distinct role in prostate cancer disparities. Low-grade chronic inflammation and an inflammatory tumor microenvironment are more prevalent in African American patients and have been associated with adverse outcomes. Thus, differences in activation of immune-inflammatory pathways between African American and European American men with prostate cancer may exist. These differences may influence the response to immune therapy which is consistent with recent observations. This review will discuss mechanisms by which inflammation may contribute to the disparate outcomes experienced by African American men with prostate cancer and how these immunogenic and inflammatory vulnerabilities could be exploited to improve their survival.

Resistance mechanisms to programmed cell death protein 1 and programmed death ligand 1 inhibitors

Introduction: In the past few years, administrating monoclonal humanized antibodies, namely checkpoint inhibitors, against programmed cell death protein 1 (PD-1), and its ligand (PD-L1), has yielded reassuring tumor regression rates. Anti-PD-1/PD-L1 checkpoint inhibitors disrupt the engagement of PD-1 on T-cells and their ligands on tumor or other target cells and reactivate the tumor-specific T infiltrating lymphocytes (TILs), which are mostly in a state of anergy before the PD-1/PD-L1 blockade. However, a limited number of patients initially respond, and the others show a primary (innate) resistance. Moreover, the rate of relapse and tumor progression after a partial, or even complete response (secondary or acquired resistance) is relatively considerable.Areas covered: This paper presents a comprehensive discussion on the mechanisms of primary and secondary resistance to PD-1/PD-L1 blockade. Loss of T-cell infiltration or T-cell exclusion, lack of PD-L1 or PD-1 expression, and also lack of tumor immunogenicity are among the most important mechanisms, and also biomarkers of resistance in patients undergoing PD-1/PD-L1 blockade. Several somatic mutations in tumors are known to be related to at least one of the resistance mechanisms.Expert opinion: Identification of the novel resistance mechanisms suggests further combinatorial therapies to tackle primary and secondary resistance to PD-1/PD-L1 blockade.

KEYNOTE-641: a Phase III study of pembrolizumab plus enzalutamide for metastatic castration-resistant prostate cancer

Current treatment options for men with metastatic castration-resistant prostate cancer (mCRPC) are noncurative, and median survival upon development of mCRPC is approximately 3 years. The novel hormonal agent enzalutamide has an established role in the mCRPC treatment paradigm, and emerging evidence suggests potential synergism with enzalutamide and the PD-1 inhibitor pembrolizumab in men with mCRPC. Here, we describe the design and rationale for the multicenter, randomized, double-blind, Phase III KEYNOTE-641 study, which will be conducted to compare the efficacy and safety of pembrolizumab plus enzalutamide with that of enzalutamide plus placebo in mCRPC. Clinical trial registration: NCT03834493 (ClinicalTrials.gov).

Immune Checkpoint Inhibitors in Prostate Cancer

Simple Summary

Metastatic prostate cancer is an incurable disease with limited treatment options. Immunotherapy has demonstrated significant success in multiple cancer types but efforts to harness its benefit in prostate cancer have so far largely been unsuccessful. In this review, we analyze the preclinical rationale for the use of immunotherapy and underlying barriers preventing responses to it. We summarize clinical studies evaluating checkpoint inhibitors in prostate cancer. In the end, we review ongoing trials exploring combination immune checkpoint inhibitors in combination with other agents with the intent to modulate the immune system to improve treatment outcomes.

Abstract

Metastatic prostate cancer is a lethal disease with limited treatment options. Immune checkpoint inhibitors have dramatically changed the treatment landscape of multiple cancer types but have met with limited success in prostate cancer. In this review, we discuss the preclinical studies providing the rationale for the use of immunotherapy in prostate cancer and underlying biological barriers inhibiting their activity. We discuss the predictors of response to immunotherapy in prostate cancer. We summarize studies evaluating immune checkpoint inhibitors either as a single agent or in combination with other checkpoint inhibitors or with other agents such as inhibitors of androgen axis, poly ADP-ribose polymerase (PARP), radium-223, radiotherapy, cryotherapy, tumor vaccines, chemotherapy, tyrosine kinase inhibitors, and granulocyte-macrophage colony-stimulating factor. We thereafter review future directions including the combination of immune checkpoint blockade with inhibitors of adenosine axis, bispecific T cell engagers, PSMA directed therapies, adoptive T-cell therapy, and multiple other miscellaneous agents.

Cell membrane and nuclear expression of programmed death ligand-1 in prostate needle biopsy tissue in prostate cancer patients undergoing primary radiation therapy

BACKGROUND

Programmed death ligand-1 (PD-L1) expression in cancer is often associated with cancer aggressiveness and responsiveness to treatment with PD-1 pathway inhibitors. We conducted a systematic study on the expression of membranous PD-L1 (mPD-L1) and nuclear PD-1-L1 (nPD-L1) in prostate needle biopsy specimens of prostate cancer patients who underwent primary radiotherapy and analyzed the association between PD-L1 expression and clinicopathological characteristics and prognosis of patients.

METHOD

A total of 971 cancer-containing prostate needle biopsy cores from 172 patients were immunohistochemically stained with anti-PD-L1 antibody. The association of PD-L1 expression with Gleason score and tumor volume percentage was evaluated for each biopsy core. Total of 171 patients were divided according to mPD-L1 or nPD-L1 expression, and clinicopathological characteristics were compared between the positive and negative groups. The prognostic significance of mPD-L1, nPD-L1 and common prognostic factors were analyzed in terms of biochemical recurrence.

RESULT

Total of 15% and 46% of biopsy cores were stained positive for mPD-L1 and nPD-L1, respectively. There was a positive correlation between Gleason score and mPD-L1 and a negative correlation between Gleason score and nPD-L1. Between mPD-L1 and nPD-L1, there was no significant correlation. There was intraindividual heterogeneity in PD-L1 expression among different Gleason scores. For mPD-L1, only pretreatment PSA was significantly higher in the positive group than in the negative, but not Gleason score and T stage. For nPD-L1, Gleason score and T stage were significantly higher in the positive group than in the negative. Both mPD-L1 and nPD-L1 expression were not predictive of BCR-free survival in univariate and multivariate analyses.

CONCLUSIONS

Our results suggest that PD-1 pathway inhibitor may be a potential therapeutic option in high risk prostate cancer patients as early as neoadjuvant setting. The novel discovery of PD-L1 expression in the nucleus of PC should be subjected to further research.

Grading Evolution and Contemporary Prognostic Biomarkers of Clinically Significant Prostate Cancer

Simple Summary

Prostate cancer treatment decisions are based on clinical stage and histological diagnosis, including Gleason grading assessed by a pathologist, in biopsies. Prior to staging and grading, serum or blood prostate-specific antigen (PSA) levels are measured and often trigger diagnostic examinations. However, PSA is best suited as a marker of cancer relapse after initial treatment. In this review, we first narratively describe the evolution of histological grading, the current status of Gleason pattern-based diagnostics and glance into future methodology of risk assessment by histological examination. In the second part, we systematically review the biomarkers that have been shown, independent from clinical characteristics, to correlate with clinically relevant end-points, i.e., occurrence of metastases, disease-specific mortality and overall survival after initial treatment of localized prostate cancer.

Abstract

Gleason grading remains the strongest prognostic parameter in localized prostate adenocarcinoma. We have here outlined the evolution and contemporary practices in pathological evaluation of prostate tissue samples for Gleason score and Grade group. The state of more observer-independent grading methods with the aid of artificial intelligence is also reviewed. Additionally, we conducted a systematic review of biomarkers that hold promise in adding independent prognostic or predictive value on top of clinical parameters, Grade group and PSA. We especially focused on hard end points during the follow-up, i.e., occurrence of metastasis, disease-specific mortality and overall mortality. In peripheral blood, biopsy-detected prostate cancer or in surgical specimens, we can conclude that there are more than sixty biomarkers that have been shown to have independent prognostic significance when adjusted to conventional risk assessment or grouping. Our search brought up some known putative markers and panels, as expected. Also, the synthesis in the systematic review indicated markers that ought to be further studied as part of prospective trials and in well characterized patient cohorts in order to increase the resolution of the current clinico-pathological prognostic factors.

Prostate cancer C5a receptor expression and augmentation of cancer cell proliferation, invasion, and PD-L1 expression by C5a

BACKGROUND

The treatment of castration-resistant prostate cancer (CRPC) is a urological issue. Recent studies have revealed cancer promotion via the C5a-C5a receptor (C5aR) system. To establish a new therapeutic target for CRPC, we investigated an association of the system with CRPC progression and evasion from the antitumor immune responses.

METHODS

C5aR and PD-L1 were immunostained in the prostate cancer (PC) tissues. The relationship of PC C5aR expression to clinicopathological parameters was analyzed. CRPC cell lines were examined for C5aR expression by real-time reverse transcription polymerase chain reaction, immunoblotting, and flow cytometry. C5a effects were examined on CRPC cell glutamine consumption, proliferation, invasion, and PD-L1 expression.

RESULTS

PC cells expressed C5aR in 83 of the 161 patients (52%) and in three of the six CRPC patients. Basal cells, but not luminal cells, of noncancerous prostate glands expressed C5aR. Three CRPC cell lines expressed C5aR. C5a increased CRPC cell glutamine consumption 2.1-fold, proliferation 1.3-1.6-fold, and invasion 2-3-fold in a C5a-concentration and a C5aR-dependent manner. High expression of C5aR did not relate to the PC patients' clinical parameters but the PD-L1-positive rate was higher in the C5aR high-expression patients (37.5%) compared to low- or no expression patients (17.8%), and double-positive PC cells were present. C5a increased CRPC cell PD-L1 production 1.4-fold and cell-surface expression 2.6-fold.

CONCLUSIONS

C5aR expression of PC cells in patients' tissues and C5a augmentation of C5aR-dependent CRPC proliferation, invasion, and PD-L1 expression suggested participation of the C5a-C5aR system in CRPC promotion and evasion from antitumor immune responses. Targeting this signaling pathway may provide a useful therapeutic option for CRPC.

Refining Immuno-Oncology Approaches in Metastatic Prostate Cancer: Transcending Current Limitations

OPINION STATEMENT

Due to its immunosuppressive tumor microenvironment, prostate cancer has historically been difficult to treat with immuno-oncology approaches. Other than pembrolizumab, which is now regulatory-approved for all microsatellite instability (MSI)-high and tumor mutational burden (TMB)-high advanced solid tumors, sipuleucel-T is the only immunotherapeutic agent approved by the US Food and Drug Administration (FDA) for prostate cancer. However, sipuleucel-T efficacy is optimal for select patients with indolent metastatic castration-resistant prostate cancer. Although manipulation of immune regulation by blocking immune checkpoints has led to substantial benefit in many cancers, experience with single-agent CTLA-4 and PD-1 or PD-L1 antibodies has shown limited effect for the majority of patients with prostate cancer, especially when administered as monotherapy. Combination therapies are now being attempted, in addition to enrichment strategies employing patient clinicopathologic and biologic characteristics that may heighten responses to immuno-oncology treatment, such as PD-L1 expression, TMB, MSI status, and alterations in CDK12. More work is needed to overcome the immune-exclusive barriers in prostate cancer, such as relatively low TMB, increased activity of myeloid-derived suppressor cells (MDSCs) and regulatory T cells, and defects in major histocompatibility complex (MHC) class I expression and interferon (IFN)-1 signaling. A promising approach and the likely next step in immuno-oncology for prostate cancer involves forced direction to markers expressed by prostate cancer tumor cells, such as prostate-specific membrane antigen (PSMA), that bypass the typical requirements for MHC class I interaction. The future will incorporate bispecific antibodies and chimeric antigen receptor (CAR)-T cells, potentially targeted towards phenotypic markers identified by next-generation PET imaging as part of the next wave of "precision medicine" in prostate cancer. Ultimately, we believe that the immune-exclusive prostate cancer tumor microenvironment can be overcome, and that patient outcomes can be enhanced through these more refined immuno-oncology approaches.

Association between CD8 and PD-L1 expression and outcomes after radical prostatectomy for localized prostate cancer

BACKGROUND

Characterization of markers of both immune suppression and activation may provide more prognostic information than assessment of single markers in localized prostate cancer. We therefore sought to determine the association between CD8 and PD-L1 expression in localized prostate tumors and biochemical recurrence (BCR) and metastasis-free survival (MFS).

METHODS

Tissue microarrays were constructed on 109 men undergoing radical prostatectomy (RP) for localized prostate cancer at Dana-Farber Cancer Institute between 1991 and 2008. Fluorescence immunohistochemistry was used to evaluate the expression of six immune markers (CD3, CD4, CD8, PD-1, PD-L1, FOXP3). Quantitative multispectral imaging analysis was used to calculate the density of each marker, which was dichotomized by the median as "high" or "low." Cox proportional hazards regression models and Kaplan-Meier analyses were used to analyze associations between immune marker densities and time to BCR and MFS.

RESULTS

Over a median follow-up of 8.1 years, 55 (51%) and 39 (36%) men developed BCR and metastases, respectively. Median time to BCR was shorter in men with low CD8 (hazard ratio [HR] = 2.27 [1.27-4.08]) and high PD-L1 expression (HR = 2.03 [1.17-3.53]). While neither low CD8 or high PD-L1 alone were independent predictors of BCR or MFS on multivariable analysis, men with low CD8 and/or high PD-L1 had a significantly shorter time to BCR (median 3.5 years vs. NR) and MFS (median 10.8 vs. 18.4 years) compared to those with high CD8 and low PD-L1 expression. The main limitation is the retrospective and singe-center nature of the study.

CONCLUSION

The presence of higher CD8 and lower PD-L1 expression in prostatectomy specimens was associated a low risk of biochemical relapse and metastatic disease. These findings are hypothesis-generating and further study is needed.

The clinicopathological significance and prognostic value of programmed death-ligand 1 in prostate cancer: a meta-analysis of 3133 patients

Background: Programmed death-ligand 1 (PD-L1) is considered an adverse factor predicting poor prognosis in various cancers, but the significance of PD-L1 expression for the prognosis of prostate cancer (PCa) is still unclear. We aimed to investigate the clinicopathological significance and prognostic value of PD-L1 expression in PCa.

Methods: Studies were retrieved from PubMed, Web of Science, Cochrane Library and Embase before March 23, 2020. Odds ratios (ORs) and hazard ratios (HRs) with 95% confidence intervals (CIs) were obtained to assess the results. Begg’s test was applied to evaluate publication bias.

Results: Fourteen studies involving 3133 cases were analyzed. The pooled data showed that both PD-L1 protein expression and PD-L1 DNA methylation (mPD-L1) were negatively associated with biochemical recurrence-free survival, with HRs of 1.67 (95% CI = 1.38-2.06, p < 0.001) and 2.23 (95% CI = 1.51-3.29, p < 0.001), respectively. In addition, PD-L1 overexpression was significantly related to advanced tumor stage (OR = 1.40, 95% CI= 1.13-1.75, p = 0.003), positive surgical margin (OR = 1.36, 95% CI = 1.03-1.78, p = 0.028), higher Gleason score (OR = 1.81, 95% CI = 1.35-2.42, p < 0.001) and androgen receptor positivity (OR = 2.20, 95% CI = 1.61-3.01, p < 0.001), while no significant correlation with age (p = 0.122), preoperative PSA (p = 0.796) or nodal status (p = 0.113) was observed.

Conclusions: The study revealed that high expression of PD-L1 was related to unfavorable prognosis and advanced clinicopathological factors in PCa patients.

High-dose per Fraction Radiotherapy Induces Both Antitumor Immunity and Immunosuppressive Responses in Prostate Tumors

PURPOSE

The use of high-dose per fraction radiotherapy delivered as stereotactic body radiotherapy is a standard of care for prostate cancer. It is hypothesized that high-dose radiotherapy may enhance or suppress tumor-reactive immunity. The objective of this study was to assess both antitumor and immunosuppressive effects induced by high-dose radiotherapy in prostate cancer coclinical models, and ultimately, to test whether a combination of radiotherapy with targeted immunotherapy can enhance antitumor immunity.

EXPERIMENTAL DESIGN

We studied the effects of high-dose per fraction radiotherapy with and without anti-Gr-1 using syngeneic murine allograft prostate cancer models. The dynamic change of immune populations, including tumor-infiltrating lymphocytes (TIL), T regulatory cells (Treg), and myeloid-derived suppressive cells (MDSC), was evaluated using flow cytometry and IHC.

RESULTS

Coclinical prostate cancer models demonstrated that high-dose per fraction radiotherapy induced a rapid increase of tumor-infiltrating MDSCs and a subsequent rise of CD8 TILs and circulating CD8 T effector memory cells. These radiation-induced CD8 TILs were more functionally potent than those from nonirradiated controls. While systemic depletion of MDSCs by anti-Gr-1 effectively prevented MDSC tumor infiltration, it did not enhance radiotherapy-induced antitumor immunity due to a compensatory expansion of Treg-mediated immune suppression.

CONCLUSIONS

In allograft prostate cancer models, high-dose radiotherapy induced an early rise of MDSCs, followed by a transient increase of functionally active CD8 TILs. However, systemic depletion of MDSC did not augment the antitumor efficacy of high-dose radiotherapy due to a compensatory Treg response, indicating blocking both MDSCs and Tregs might be necessary to enhance radiotherapy-induced antitumor immunity.

The expression and prognostic relevance of programmed cell death protein 1 in tongue squamous cell carcinoma

Programmed cell death protein 1 (PD-1) is an immune checkpoint receptor which plays an important role in a patient's immune responses to microbial and cancer antigens. It is expressed in tumor-infiltrating lymphocytes (TILs) with many different malignancies. The aim of the study was to evaluate PD-1 expression and its prognostic value in tongue cancer. The data of tongue squamous cell carcinoma (TSCC) patients (N = 81) treated in Tampere University Hospital between 1999 and 2013 were used. Control data consisted of patients with non-malignant tongue mucous membrane lesions (N = 48). The formalin-fixed paraffin-embedded samples were stained immunohistochemically and scanned via digital microscope. The staining of PD-1 was examined semi-quantitatively. The density and intensity of PD-1 + cells were significantly higher in TSCC than in control samples. The expression of PD-1 correlated with better survival. The expression of PD-1 could be a potential prognostic marker in TSCC. Further research using larger sample size is needed.

Immunotherapy in prostate cancer: current state and future perspectives

Metastatic castrate resistant prostate cancer (PCa) remains an incurable entity. In the era of immunotherapy, the complex PCa microenvironment poses a unique challenge to the successful application of this class of agents. However, in the last decade, a tremendous effort has been made to explore this field of therapeutics. In this review, the physiology of the cancer immunity cycle is highlighted in the context of the prostate tumor microenvironment, and the current evidence for use of various classes of immunotherapy agents including vaccines (dendritic cell based, viral vector based and DNA/mRNA based), immune checkpoint inhibitors, Chimeric antigen receptor T cell therapy, antibody-mediated radioimmunotherapy, antibody drug conjugates, and bispecific antibodies, is consolidated. Finally, the future directions for combinatorial approaches to combat PCa are discussed.

LncRNA KCNQ1OT1 sponges miR-15a to promote immune evasion and malignant progression of prostate cancer via up-regulating PD-L1

Background

We focused on the KCNQ1OT1/miR-15a/PD-L1 axis and explored its significance in regulating immune evasion and malignant behaviors of prostate cancer (PC) cells.

Methods

The expression levels of KCNQ1OT1, miR-15a, PD-L1, and CD8 in cells or tissues were examined by RT-qPCR, western blot or immunohistochemistry (IHC) assays. The direct regulations between KCNQ1OT1, miR-15a and PD-L1 were validated by luciferase reporter assay. PC cells were co-cultured with CD8⁺ T cells to study the immune evasion. Proliferation, apoptosis, migration and invasion abilities were detected by MTT, flow cytometry, wound healing and Transwell assays, respectively. The cytotoxicity of CD8⁺ T cells was determined by LDH cytotoxicity Kit. Epithelial–mesenchymal transition (EMT) and Ras/ERK signaling markers were evaluated by western blot.

Results

KCNQ1OT1, PD-L1 and CD8 were increased, while miR-15a was decreased in PC tissues. MiR-15a directly bound to the 3′-UTR of PD-L1 and inhibited the expression of PD-L1. Overexpressing miR-15a in PC cells was sufficient to promote cytotoxicity and proliferation, while inhibit apoptosis of CD8⁺ T cells, and also suppressed viability, migration, invasion and EMT while promoted apoptosis of PC cells. The above anti-tumor effects of miR-15a were reversed by overexpressing PD-L1. KCNQ1OT1 sponged miR-15a and released its inhibition on PD-L1. Functionally, KCNQ1OT1 in PC cells was essential for suppressing the cytotoxicity of CD8⁺ T cells and maintaining multiple malignant phenotypes of PC cells. The Ras/ERK signaling was suppressed after overexpressing miR-15a or knocking down KCNQ1OT1.

Conclusions

LncRNA KCNQ1OT1 sponges miR-15a to promote immune evasion and malignant progression of PC via up-regulating PD-L1.

Immunotherapy in Prostate Cancer

Immunotherapy encompasses a wide range of therapies to engage the immune system to target malignancies. In recent years, immunotherapy has made a major impact on treatment of metastatic cancer and has altered standard of care for many tumor types. However, predicting and understanding responses across tumor types has been challenging. While some metastatic cancers have shown dramatic responses to immunotherapy, such as melanoma, lung cancer, and renal cell carcinoma, prostate cancer has generally failed to show a significant response. However, small series of prostate cancer patients have shown impressive responses to cellular and immunotherapy. This review summarizes the current data for immunotherapy’s use in prostate cancer, as well as how currently available data might help predict patient responses to immunotherapy. Specifically, we will review vaccine-based therapies, immune checkpoint inhibitors, and future directions that are actively being explored.

Chemerin Reactivates PTEN and Suppresses PD-L1 in Tumor Cells via Modulation of a Novel CMKLR1-mediated Signaling Cascade

PURPOSE

Chemerin (retinoic acid receptor responder 2, RARRES2) is an endogenous leukocyte chemoattractant that recruits innate immune cells through its receptor, ChemR23. RARRES2 is widely expressed in nonhematopoietic tissues and often downregulated across multiple tumor types compared with normal tissue. Recent studies show that augmenting chemerin in the tumor microenvironment significantly suppresses tumor growth, in part, by immune effector cells recruitment. However, as tumor cells express functional chemokine/chemoattractant receptors that impact their phenotype, we hypothesized that chemerin may have additional, tumor-intrinsic effects.

EXPERIMENTAL DESIGN

We investigated the effect of exogenous chemerin on human prostate and sarcoma tumor lines. Key signaling pathway components were elucidated using qPCR, Western blotting, siRNA knockdown, and specific inhibitors. Functional consequences of chemerin treatment were evaluated using in vitro and in vivo studies.

RESULTS

We show for the first time that human tumors exposed to exogenous chemerin significantly upregulate PTEN expression/activity, and concomitantly suppress programmed death ligand-1 (PD-L1) expression. CMKLR1 knockdown abrogated chemerin-induced PTEN and PD-L1 modulation, exposing a novel CMKLR1/PTEN/PD-L1 signaling cascade. Targeted inhibitors suggested signaling was occurring through the PI3K/AKT/mTOR pathway. Chemerin treatment significantly reduced tumor migration, while significantly increasing T-cell-mediated cytotoxicity. Chemerin treatment was as effective as both PD-L1 knockdown and the anti-PD-L1 antibody, atezolizumab, in augmenting T-cell-mediated tumor lysis. Forced expression of chemerin in human DU145 tumors significantly suppressed in vivo tumor growth, and significantly increased PTEN and decreased PD-L1 expression.

CONCLUSIONS

Collectively, our data show a novel link between chemerin, PTEN, and PD-L1 in human tumor lines, which may have a role in improving T-cell-mediated immunotherapies.

PD-L1 Expression in De Novo Metastatic Castration-sensitive Prostate Cancer

De novo metastatic castration-sensitive prostate cancer (mCSPC) is small subgroup of prostate cancer associated with poor prognosis. The aim of our study was to assess the expression of programmed death-ligand 1 (PD-L1) in tumor cells of de novo mCSPC patients. Patients referred to our institution from January 2007 to October 2017 with de novo mCSPC and available diagnostic tissue were included. We tested the PD-L1 pharmaDx qualitative immunohistochemical assay, a monoclonal rabbit anti-PD-L1, clone 28-8 intended for use in the detection of PD-L1 protein in formalin-fixed paraffin-embedded. Kaplan-Meier method was used to estimate survivals according to the expression of PD-L1. The study population included 32 de novo mCSPC patients, analyzed for PD-L1 expression using 2 cut-off values (1% and 5%) to define the positivity. Total of 46.9% of cases had tumor PD-L1 expression ≥1%, and 31.3% had expression ≥5%. No differences were found between the PD-L1 expression ≥1% and the involvement of liver, lung, and number of bone metastases, and the disease volume based on CHAARTED classification. PD-L1 tumors had higher incidence of Gleason score ≥8 compared with PD-L1 tumors (P=0.037), while the incidence of lymph node metastases was higher in PD-L1 tumors (P=0.044). No difference in the median overall survival (mOS) was observed between the PD-L1 population and the PD-L1 patients (43.8 vs. 29.6 mo; P=0.88). The tumor PD-L1 expression cannot be considered a prognostic factor for de novo mCSPC, even if its prognostic and predictive significance have to be thoroughly investigated to better define the selected group of prostate cancer patients that might benefit from checkpoint blockade immunotherapy.

Immunohistochemistry of immune checkpoint markers PD-1 and PD-L1 in prostate cancer

Recent availability of immune checkpoint inhibitors has facilitated research involving programmed cell death protein 1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1). However, the incidence and clinical implication of PD-1 and PD-L1 expression in prostate cancer remain poorly understood. The current study aimed to determine the status of PD-1/PD-L1 expression in prostate cancer specimens and its prognostic significance.We immunohistochemically stained for PD-1 and PD-L1 in our tissue microarray (TMA) consisting of radical prostatectomy specimens. The expression of PD-1/PD-L1 was designated as positive when moderate to strong staining or weak staining was seen in at least 1% or 10%, respectively, of tumor cells and/or associated immune cells. We then evaluated the relationship between the expression of each protein and clinicopathological features available for our patient cohort.PD-1 and PD-L1 were positive in 3 (1.5%) and 1 (0.5%) of 201 non-neoplastic prostate tissues, and also in 17 (7.7%) and 29 (13.2%) of 220 prostate cancers, respectively. PD-1 and PD-L1 were also expressed in tumor-infiltrating lymphocytes/macrophages in 172 (78.2%) and 33 (15.0%) cases, respectively. PD-L1 expression in tumor cells was more often seen in high pT stage (pT2: 10.8% vs pT3/4: 20.4%; P = .072; pT2/3a: 11.4% vs pT3b/4: 31.6%; P = .013) or lymph node-positive (pN0: 10.1% vs pN1: 27.3%; P = .086) cases, whereas PD-1 expression in tumor cells was not significantly associated with pT/pN stage. In addition, there were no statistically significant associations between PD-1/PD-L1 expression in tumor cells or tumor-infiltrating lymphocytes/macrophages versus patient age, preoperative prostate-specific antigen level, or Gleason score. Kaplan-Meier analysis coupled with log-rank test further revealed no significant associations between PD-1/PD-L1 expression in tumor cells (P = .619/P = .315), tumor-infiltrating lymphocytes/macrophages (P = .954/P = .155), or either or both of them (P = .964/P = .767) versus disease recurrence after radical prostatectomy.PD-1/PD-L1 expression was detected in a subset of prostate cancers. In particular, PD-L1 expression was considerably up-regulated in nonorgan-confined tumors. However, PD-1/PD-L1 expression in our TMA was found to be not very helpful in predicting tumor recurrence in prostate cancer patients who underwent radical prostatectomy.

Cellular and Molecular Mechanisms Underlying Prostate Cancer Development: Therapeutic Implications

Prostate cancer is the most frequent nonskin cancer and second most common cause of cancer-related deaths in man. Prostate cancer is a clinically heterogeneous disease with many patients exhibiting an aggressive disease with progression, metastasis, and other patients showing an indolent disease with low tendency to progression. Three stages of development of human prostate tumors have been identified: intraepithelial neoplasia, adenocarcinoma androgen-dependent, and adenocarcinoma androgen-independent or castration-resistant. Advances in molecular technologies have provided a very rapid progress in our understanding of the genomic events responsible for the initial development and progression of prostate cancer. These studies have shown that prostate cancer genome displays a relatively low mutation rate compared with other cancers and few chromosomal loss or gains. The ensemble of these molecular studies has led to suggest the existence of two main molecular groups of prostate cancers: one characterized by the presence of ERG rearrangements (~50% of prostate cancers harbor recurrent gene fusions involving ETS transcription factors, fusing the 5' untranslated region of the androgen-regulated gene TMPRSS2 to nearly the coding sequence of the ETS family transcription factor ERG) and features of chemoplexy (complex gene rearrangements developing from a coordinated and simultaneous molecular event), and a second one characterized by the absence of ERG rearrangements and by the frequent mutations in the E3 ubiquitin ligase adapter SPOP and/or deletion of CDH1, a chromatin remodeling factor, and interchromosomal rearrangements and SPOP mutations are early events during prostate cancer development. During disease progression, genomic and epigenomic abnormalities accrued and converged on prostate cancer pathways, leading to a highly heterogeneous transcriptomic landscape, characterized by a hyperactive androgen receptor signaling axis.

PD-L1 expression and deficient mismatch repair in ductal adenocarcinoma of the prostate

This study aimed to investigate the expression of programmed death receptor ligand 1 (PD-L1) and deficient mismatch repair (dMMR) in ductal adenocarcinoma of the prostate. A tissue microarray of 32 ductal and 42 grade-matched acinar adenocarcinomas was used. Slides were stained for PD-L1, PD-L2, MMR proteins, CD4 and CD8. PD-L1 expression in tumor cells was only seen in 3% (1/34) of ductal and 5% (2/42) of acinar adenocarcinomas (p = 1.0), while PD-L1 expression in tumor-infiltrating immune cells was seen in 29% (10/34) of ductal and 14% (6/42) of acinar adenocarcinomas (p = 0.16). dMMR, as defined by loss of one or more of the MMR proteins, was identified in 5% (4/73) of cases, including 1 ductal and 3 acinar adenocarcinomas. There was a suggested association between infiltration of CD8+ lymphocytes and ductal subtype (p = 0.04) but not between CD4+ lymphocytes and tumor type (p = 0.28). The study shows that both dMMR and PD-L1 expression is uncommon in tumor cells of both ductal and acinar adenocarcinoma of the prostate, while PD-L1 expression in tumor-infiltrating immune cells is a more common finding.

Low Expression of miR-424-3p is Highly Correlated with Clinical Failure in Prostate Cancer

Prostate cancer (PC) is a highly heterogenous disease and one of the leading causes of mortality in developed countries. Recently, studies have shown that expression of immune checkpoint proteins are directly or indirectly repressed by microRNAs (miRs) in many types of cancers. The great advantages of using miRs based therapy is the capacity of these short transcripts to target multiple molecules for the same- or different pathways with synergistic immune inhibition effects. miR-424 has previously been described as a biomarker of poor prognosis in different types of cancers. miR-424 is also found to target both the CTLA-4/CD80- and PD-1/PD-L1 axis. In the present study, the clinical significance of miR-424-3p expression in PC tissue was evaluated. Naïve radical prostatectomy specimens from 535 patients was used for tissue microarray construction. In situ hybridization was used to evaluate the expression of miR-424-3p and immunohistochemistry was used for CTLA-4 protein detection. In univariate- and multivariate analyses, low expression of miR-424-3p was significant associated with clinical failure-free survival, (p = 0.004) and p = 0.018 (HR:0.44, CI95% 0.22-0.87). Low expression of miR-424-3p also associated strongly with aggressive phenotype of PC. This highlight the importance of miR-424-3p as potential target for therapeutic treatment in prostate cancer.

PD-L1 instead of PD-1 status is associated with the clinical features in human primary prostate tumors

Immunotherapy targeting programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) has shown efficacy in a variety of solid tumors. However, prostate cancer has often been a non-responder to anti-PD-1/PD-L1 therapies. The objective of this study was to determine PD-1 and PD-L1 expression status and its correlation with clinical features of the patients. A total of 279 patients who underwent radical prostatectomy for prostate cancer were included in this study. PD-1 and PD-L1 expression in primary prostate tumors was detected using immunohistochemical staining. Analyses were made between PD-1/PD-L1 status and patients' age, ethnicity, body mass index (BMI), diabetes mellitus, tumor stage, lymph node metastasis, prostate-specific antigen (PSA), Gleason score, grade group, and survival. We found that 6.5 (standard deviation 14.3; range 0-161.6) tumor-infiltrating lymphocytes per high power field were positive for PD-1 staining and 50/279 (17.9%) tumors were positive for PD-L1 staining. PD-L1-positive tumors had significantly more PD-1-positive lymphocytes than PD-L1-negative tumors. The number of PD-1-positive lymphocytes was not correlated with any clinical features except that patients with diabetes had significantly less PD-1-positive lymphocytes than patients without diabetes. In contrast, more PD-L1-positive tumors were found in older patients (≥ 65 years), obese patients (BMI ≥ 30), and patients with advanced tumor stage, lymph node metastasis, and high Gleason score. Neither PD-1 nor PD-L1 status was correlated with ethnicity, PSA, or survival. Our findings suggest that PD-L1 instead of PD-1 status is associated with the clinical features in human primary prostate tumors.

The Immune Checkpoint Regulator PDL1 is an Independent Prognostic Biomarker for Biochemical Recurrence in Prostate Cancer Patients Following Adjuvant Hormonal Therapy

Background: The programmed death 1 (PD1)/programmed death ligand 1 (PDL1) targeted therapies have gained positive outcomes in several tumors, but the evidence of the expression and prognosis value of PD1/PDL1 in high risk prostate cancer was rare.

Methods: Immunohistochemical analysis of PDL1/PD1 expression by a validated antibody was performed in a retrospectively collected high risk prostate cancer cohort who received adjuvant hormonal therapy (AHT) after radical prostatectomy (RP). The association between PDL1/PD1 expression and prognosis was determined.

Results: In total, 127 patients were enrolled. 49.6% patients were considered PDL1-high expression while the PD1-positive expression proportion was 24.4%. High PDL1 and negative PD1 expression were significantly associated with lower prostate specific antigen (PSA) density (p=0.010 and p=0.033, respectively). Compared with the PDL1-low expression patients, the PDL1-high expression patients had significantly shorter time to PSA nadir (TTN) (P=0.001) and biochemical recurrence (BCR) (P=0.004). In Kaplan-Meier analysis, the PDL1-high expression group (p<0.0001) and the PDL1-high/PD1-negative expression group (p<0.0001) showed markedly lower BCR-free survival in localized disease. Univariate cause-specific Cox proportional hazard regression model concluded total PSA (p=0.047), PDL1-high-expression (p<0.001), PDL1-high/PD1-negative expression (p<0.001) were significant risk factors of shorter progression time to BCR in localized disease. PDL1-high-expression was the independent predictor of time to BCR in multiple Cox regression of all patients (Hazard ratio [HR]: 3.901; 95% Confidence interval [CI]: 1.287-11.824; p=0.016).

Conclusions: PDL1 expression is not only highly prevalent in high-risk prostate cancer, but is also an independent biomarker in the prognosis of high-risk prostate cancer received AHT after RP. PDL1/PD1 targeted therapy might be a potentially adjuvant treatment option for high-risk prostate cancer after RP.

The Clinicopathologic and Prognostic Significance of Programmed Cell Death Ligand 1 (PD-L1) Expression in Patients With Prostate Cancer: A Systematic Review and Meta-Analysis

Background: Programmed cell death ligand 1 (PD-L1) expression has been shown to correlate with poor prognosis in diverse human cancers. However, limited data exist on the prognostic and clinicopathologic significance of PD-L1 expression in prostate cancers (PCa), and the curative effect of anti-PD-1/PD-L1 therapy remains controversial. In this systematic review and meta-analysis, we aimed to evaluate the prognostic and clinicopathologic value of PD-L1 in PCa. Methods: We performed a systematic literature search in the PubMed, Cochrane Library, EMBASE, Web of Science, and SCOPUS databases up to July 21st, 2018. Pooled prevalence of PD-L1 in PCa was calculated using Freeman-Tukey double arcsine transformation by R software version 3.5.0. The data from the studies were examined by a meta-analysis using Review Manager software 5.3 to calculate pooled hazard ratios (HRs) and pooled odds ratios (ORs) with 95% confidence intervals (CIs) to estimate the prognostic and clinicopathologic value of PD-L1 in PCa. Heterogeneity was tested by the Chi-squared test and I ² statistic. Results: Five studies with 2,272 patients were included in this meta-analysis. The pooled prevalence of PD-L1 in PCa was 35% (95% CI 0.32 to 0.37). Both PD-L1 expression (HR = 1.78; 95% CI 1.39 to 2.27; p < 0.00001) and PD-L1 DNA methylation (HR = 2.23; 95% CI 1.51 to 3.29; p < 0.0001) were significantly associated with poor biochemical recurrence-free survival (BCR-FS). PD-L1 tended to have high expression levels in high Gleason score cases (OR = 1.54; 95% CI, 1.17 to 2.03; P = 0.002) and androgen receptor-positive cases (OR = 2.42, 95% CI 1.31 to 4.50; P = 0.005). However, PD-L1 had relatively weak correlation with age, pathologic stage, lymph node metastasis and preoperative PSA level. Conclusions: This meta-analysis confirms the negative prognostic significance of PD-L1 expression and mPD-L1 in PCa patients. Additionally, PD-L1 has a statistically significant correlation with Gleason score and androgen receptor status, while the correlations with age, pathologic stage, lymph node metastasis, and preoperative PSA level were not statistically significant. However, the number of included studies is too small to make the conclusions more convincing, so more retrospective large-cohort studies are expected for the further confirmation of these findings.

Prognostic value of PD-L1 expression in resected lung adenocarcinoma and potential molecular mechanisms

Background: The prognostic role of PD-L1 expression in surgically resected lung adenocarcinoma (ADC) remains controversial. The present study was aimed to clarify the role of PD-L1 expression in predicting prognosis and to investigate its biological function in ADC.

Materials and Methods: The association between PD-L1 expression and clinical outcomes in patients with resected ADC was analyzed using immunohistochemistry (IHC) in our cohort (n=104), externally validated by a meta-analysis of 13 published studies. The biological role of PD-L1 in ADC was explored using gene set enrichment analysis (GSEA).

Results: Positive PD-L1 expression in tumor cells was observed in 38.5% (40/104). High PD-L1 expression levels were significantly correlated with poor overall survival (P=0.008). Furthermore, the meta-analysis also showed that positive PD-L1 expression was associated with shorter OS than negative PD-L1 expression (HR= 1.75, 95% CI: 1.26-2.42; P<0.001). In subgroup analysis stratified according to ethnicity, the pooled results demonstrated that increased PD-L1 expression was an unfavorable prognostic factor for Asian populations (HR= 2.11, 95% CI: 1.48-3.02; P<0.001), but not for non-Asian populations (HR=1.16, 95% CI: 0.63-2.11, P=0.64). The pooled odds ratios (ORs) indicated that PD-L1 expression was associated with positive lymph node metastasis (OR=1.74, 95% CI: 1.23-2.46; P=0.002) and male (OR=1.56, 95% CI: 1.02-2.37; P=0.04). GSEA revealed PD-L1 expression levels positively correlated with immune process or immune-related pathways.

Conclusion: PD-L1 expression is an important negative prognostic factor in resected ADC. This finding has important implications for immunotherapy targeting the PD-1/PD-L1 pathway in patients with resected ADC.