The Immune Microenvironment, Genome-wide Copy Number Aberrations, and Survival in Mesothelioma

Evaluation of first-line and salvage therapies for unresectable malignant mesothelioma: A systematic review and network meta-analysis

BACKGROUND

Randomized controlled trials (RCTs) of systemic therapies for unresectable malignant mesothelioma have reported conflicting results. It is crucial and urgent to find optimal treatment options for this malignancy, which currently has a poor prognosis.

METHODS

Databases PubMed, EMBASE, Cochrane Library, ClinicalTrials.gov, and major international conferences were searched until February 29, 2024. The main outcomes of interest were overall survival (OS), progression-free survival (PFS), overall response rate (ORR), and grade ≥3 treatment-related adverse events (TRAEs).

RESULTS

We analyzed 16 RCTs with a total of 5018 patients. Among first-line therapies, nivolumab and ipilimumab significantly increased OS and resulted in fewer grade ≥3 TRAEs. Bevacizumab plus chemotherapy significantly increased PFS. Among salvage therapies, ramucirumab and chemotherapy was associated with the best OS and PFS, but resulted in more grade ≥3 TRAEs. Subgroup analysis by histologic types suggested that in first-line settings, bevacizumab and chemotherapy increase OS the most for epithelioid type, while the nivolumab plus ipilimumab treatment increases OS the most for non-epithelioid type. In salvage therapies, ramucirumab and chemotherapy increase OS for both epithelioid and non-epithelioid types.

CONCLUSION

Nivolumab plus ipilimumab was associated with the best OS among first-line treatments. Ramucirumab and chemotherapy was associated with the best clinical outcomes in salvage settings. Treatment for malignant mesothelioma should be tailored based on different clinicopathological characteristics.

Molecular and Immunohistochemical Testing in Mesothelioma and Other Mesothelial Lesions

CONTEXT.—

Molecular testing has increasingly been utilized in the evaluation of mesothelioma. Diffuse mesothelioma comprises multiple distinct genetic subgroups. While most diffuse mesotheliomas lack oncogenic kinase mutations and instead harbor alterations involving tumor suppressors and chromatin regulators, a minor subset of tumors is characterized by uncommon alterations such as germline mutations, genomic near-haploidization, ALK rearrangement, ATF1 rearrangement, or EWSR1::YY1 fusion.

OBJECTIVE.—

To provide updates on the salient molecular features of diffuse mesothelioma, mesothelioma in situ, and other mesothelial lesions: well-differentiated papillary mesothelial tumor, adenomatoid tumor, peritoneal inclusion cyst, and others. We consider the diagnostic, prognostic, and predictive utility of molecular testing in mesothelial lesions.

DATA SOURCES.—

We performed a literature review of recently described genetic features, molecular approaches, and immunohistochemical tools, including BAP1, MTAP, and merlin in mesothelioma and other mesothelial lesions.

CONCLUSIONS.—

Our evolving understanding of the molecular diversity of diffuse mesothelioma and other mesothelial lesions has led to considerable changes in pathology diagnostic practice, including the application of immunohistochemical markers such as BAP1, MTAP, and merlin (NF2), which are surrogates of mutation status. In young patients and/or those without significant asbestos exposure, unusual mesothelioma genetics such as germline mutations, ALK rearrangement, and ATF1 rearrangement should be considered.

Current State-of-the-Art Therapy for Malignant Pleural Mesothelioma and Future Options Centered on Immunotherapy

Malignant pleural mesothelioma (MPM) is a locally aggressive disease related to asbestos exposure with a median survival for untreated patients of 4-8 months. The combination of chemotherapy based on platinum and antifolate is the standard treatment, and the addition of bevacizumab adds two months to median survival. Recently, in first-line treatment, immunotherapy combining nivolumab with ipilimumab has been shown to be superior to chemotherapy in the CheckMate-743 study in terms of overall survival (18.1 months), leading to its approval by the FDA and EMA. The positive results of this study represent a new standard of treatment for patients with MPM; however, not all patients will benefit from immunotherapy treatment. In an effort to improve the selection of patient candidates for immunotherapy for different tumors, biomarkers that have been associated with a greater possibility of response to treatment have been described. MPM is a type of tumor with low mutational load and neo-antigens, making it a relatively non-immunogenic tumor for T cells and possibly less susceptible to responding to immunotherapy. Different retrospective studies have shown that PD-L1 expression occurs in 20-40% of patients and is associated with a poor prognosis; however, the predictive value of PD-L1 in response to immunotherapy has not been confirmed. The purpose of this work is to review the state of the art of MPM treatment in the year 2023, focusing on the efficacy results of first-line or subsequent immunotherapy studies on patients with MPM and possible chemo-immunotherapy combination strategies. Additionally, potential biomarkers of response to immunotherapy will be reviewed, such as histology, PD-L1, lymphocyte populations, and TMB.

Effects of tumor-infiltrating CD8+ T cells, PD1/PD-L1 axis, and expression patterns of HLA class I on the prognosis of patients with malignant pleural mesothelioma who underwent extra-pleural pneumonectomy

Programmed cell death protein-1 (PD1), PD1 ligand 1 (PD-L1), and human leukocyte antigen (HLA) class I molecule play pivotal roles in T cell-induced anti-tumor immunity; however, the clinical impact of these parameters in resected malignant pleural mesothelioma (MPM) cases is unknown. We immunohistochemically evaluated the tumor infiltrated lymphocytes (TILs), PD1/PD-L1 axis, and expression of HLA class I in resected specimens from 58 patients with MPM who underwent extra-pleural pneumonectomy (EPP). Higher infiltration of CD3-TIL, CD8-TIL, and PD1-TIL, loss of HLA class I, and overexpression of PD-L1 by tumor cells (PD-L1 TC) or immune cells (PD-L1 IC) were observed in 34 (58.6%), 27 (46.6%), 41 (70.7%), 45 (77.6%), 29 (50.0%), and 33 (56.4%) of 58 cases, respectively. Interestingly, the CD3-TIL score positively correlated with PD-L1 TC and PD1-TIL scores. HLA class I expression level was inversely correlated with the expression levels of PD-L1 TC and PD-L1 IC. Multivariate analysis showed that age, histology, and node metastasis were independent prognostic factors for 5-year overall survival (OS) and loss of HLA class I coincided with a positive prognosis (p = 0.011). The concomitant lack of infiltrating CD8+ T cells with no loss of HLA class I predicted worse 5-year OS (p = 0.007). Moreover, cluster classifications among multiple immunoparameters showed that categories among CD3/PD-L1 TC/HLA class I (p = 0.043), CD8/PD1/HLA class I (p = 0.032), CD8/PD-L1 TC/HLA class I (p = 0.011), and PD1/PD-L1 TC/HLA class I (p = 0.032) predicted 5-year OS in EPP cases for MPM. These immunoparameters could guide surgical indications for patients with MPM.

Preoperative neutrophil-to-lymphocyte ratio correlates with PD-L1 expression in immune cells of patients with malignant pleural mesothelioma and predicts prognosis

We assessed the prognostic value of five complex inflammatory and nutritional parameters, namely neutrophil-to-lymphocyte ratio (NLR), prognostic nutritional index (PNI), C-reactive protein-to-NLR ratio (C/NLR), platelet-to-lymphocyte ratio (PLR), and lymphocyte-to-monocyte ratio (LMR) using data from patients with malignant pleural mesothelioma (MPM) undergoing extrapleural pneumonectomy (EPP). Moreover, the correlation between these five parameters and programmed cell death protein 1 ligand-1 (PD-L1) expression in the tumor microenvironment was evaluated. This study included consecutive MPM patients who underwent EPP. The histological subtype of the eligible patients (n = 61) correlated with all five parameters. Moreover, the PD-L1 expression scores for immune cells correlated with NLR and PLR, and the PD-L1 expression scores for both tumor cells and immune cells were inversely correlated with both PNI and LMR. Univariate analysis elucidated that NLR, PNI, and C/NLR were predictors of 5-year overall survival (OS), and multivariate analysis revealed that NLR was an independent predictor of 5-year OS, suggesting that NLR is a preoperative, prognostic factor for patients with MPM who are scheduled for EPP. To the best of our knowledge, this is the first study to evaluate the prognostic potentials of NLR, PNI, C/NLR, PLR, and LMR simultaneously in patients with MPM who underwent EPP.

Investigation on the regulatory T cells signature and relevant Foxp3/STAT3 axis in esophageal cancer

BACKGROUND

Regulatory T cells (Tregs) have an important role in accelerating the immunosuppression of tumor. Tregs regulation is a hopeful strategy to improve the dismal prognosis of Esophageal cancer (EC), while its mechanisms have not yet been fully clarified.

METHODS

To characterize the role of Tregs in EC, we comprehensively explored its prognostic value, clinical pathology partnership, related biological functions and potential mechanisms at transcriptome level. Through the integrated analysis of GEO and TCGA datasets, we comprehensively evaluated the Tregs infiltration patterns in EC patients. The correlation between Tregs infiltration and genomic characteristics, as well as biological functions were analyzed by a variety of computational algorithms.

RESULTS

We observed that Tregs were significantly upregulated in EC and involved in various immune processes. According to TCGA and GEO transcriptional classification schemes, Tregs specific genes were observed to be highly expressed in tumor samples, as well as were closely associated with poor prognosis and worse clinical outcomes. In addition, EC patients can be stratified into high-risk and low-risk immune subgroups according to Tregs/macrophages infiltration level, and the results showed significant differences in tumor development, biological processes and probe gene expression pattern. The multi-variate analysis revealed that the interaction between STAT3 and Foxp3 was a potential prognostic signature of Tregs in EC, especially the modulation effect of STAT3 on Foxp3 expression, which has not been well studied in EC. We also identified that STAT3 and Foxp3 expression presented a high accuracy in predicting Tregs infiltration level in EC patients (AUC: 0.817; 95% CI: 0.756-0.878).

CONCLUSIONS

Our results revealed that Tregs have the potential to predict prognosis and tumor deterioration in EC patients. A comprehensive landscape of Tregs regulation mechanisms will help us interpret the immunosuppression of tumor microenvironment (TME) and novel strategies for EC immunotherapy.

Immunotherapy approaches for malignant pleural mesothelioma

Over the past decade, immune-checkpoint inhibitors (ICIs) have revolutionized the treatment of cancer. In mesothelioma, a rare cancer with a dismal prognosis generally caused by exposure to asbestos, treatment with single or dual ICIs results in robust improvements in overall survival over previous standard-of-care therapies, both in the first-line and relapsed disease settings. Predictive biological features that underpin response to ICIs remain poorly understood; however, insights into the immune microenvironment and genomic landscape of mesothelioma as well as into their association with response or acquired resistance to ICIs are emerging. Several studies of rational combinations involving ICIs with either another ICI or a different agent are ongoing, with emerging evidence of synergistic antitumour activity. Non-ICI-based immunotherapies, such as peptide-based vaccines and mesothelin-targeted chimeric antigen receptor T cells, have demonstrated promising efficacy. Moreover, results from pivotal trials of dendritic cell vaccines and viral cytokine delivery, among others, are eagerly awaited. In this Review, we comprehensively summarize the key steps in the development of immunotherapies for mesothelioma, focusing on strategies that have led to randomized clinical evaluation and emerging predictors of response. We then forecast the future treatment opportunities that could arise from ongoing research.

Microbiomes, Epigenomics, Immune Response, and Splicing Signatures Interplay: Potential Use of Combination of Regulatory Pathways as Targets for Malignant Mesothelioma

Malignant mesotheliomas (MM) are hard to treat malignancies with poor prognosis and high mortality rates. This cancer is highly misdiagnosed in Sub-Saharan African countries. According to literature, the incidence of MM is likely to increase particularly in low-middle-income countries (LMICs). The burden of asbestos-induced diseases was estimated to be about 231,000 per annum. Lack of awareness and implementation of regulatory frameworks to control exposure to asbestos fibers contributes to the expected increase. Exposure to asbestos fibers can lead to cancer initiation by several mechanisms. Asbestos-induced epigenetic modifications of gene expression machinery and non-coding RNAs promote cancer initiation and progression. Furthermore, microbiome-epigenetic interactions control the innate and adaptive immunity causing exacerbation of cancer progression and therapeutic resistance. This review discusses epigenetic mechanisms with more focus on miRNAs and their interaction with the microbiome. The potential use of epigenetic alterations and microbiota as specific biomarkers to aid in the early detection and/or development of therapeutic targets is explored. The advancement of combinatorial therapies to prolong overall patient survival or possible eradication of MM especially if it is detected early is discussed.

Breast Cancer during Pregnancy as a Special Type of Early-Onset Breast Cancer: Analysis of the Tumor Immune Microenvironment and Risk Profiles

Breast cancer during pregnancy (PrBC) is a rare tumor with only a little information on its immune landscape. Here, we sought to characterize the cellular composition of the tumor microenvironment (TME) of PrBC and identify its differences from early-onset breast cancer (EOBC) in non-pregnant women. A total of 83 PrBC and 89 EOBC were selected from our Institutional registry and subjected to tumor-infiltrating lymphocytes (TILs) profiling and immunohistochemistry for CD4, CD8, forkhead box P3 (FOXP3), and programmed death-ligand 1 (PD-L1) (clone 22C3). A significantly lower frequency of hormone receptor (HR)-positive tumors was observed in PrBC. The prevalence of low/null PD-L1 and CD8+TILs was higher in PrBC than in the controls, specifically in HR+/HER2– breast cancers. PrBC had a significantly higher risk of relapse and disease-related death, compared to EOBC. The presence of TILs and each TIL subpopulation were significantly associated with disease relapse. Moreover, the death rate was higher in PrBC with CD8+ TILs. The TME of PrBC is characterized by specific patterns of TIL subpopulations with significant biological and prognostic roles. Routine assessment of TILs and TILs subtyping in these patients would be a valid addition to the pathology report that might help identify clinically relevant subsets of women with PrBC.

Evolving Landscape of Initial Treatments for Patients with Malignant Pleural Mesotheliomas: Clinical Trials to Clinical Practice

Malignant pleural mesothelioma (MPM) is the most common form of mesothelioma and the type most often studied in prospective clinical trials.This review reports the trials that have shaped first-line treatment for patients with advanced/unresectable MPM and the real-world integration of first-line immune checkpoint inhibitors into clinical practice.

Tsunami of immunotherapy reaches mesothelioma

Malignant pleural mesothelioma (MPM) is the most common type of malignant mesothelioma. It is a rare tumor linked to asbestos exposure and is associated with a poor prognosis. Until very recently, patients with advanced or unresectable disease had limited treatment options, primarily based on doublet chemotherapy with cisplatin and pemetrexed. In 2020 and 2021, after more than a decade with no major advances or new drugs, two phase III clinical trials published results positioning immunotherapy as a promising option for the first- and second-line treatment of MPM. Immunotherapy has revolutionized the treatment of many cancers and is also showing encouraging results in malignant mesothelioma. Both immune checkpoint inhibition and dual cytotoxic T-lymphocyte–associated antigen 4 and programmed death-ligand 1 pathway blockade resulted in significantly improved overall survival in randomized phase III trials. In the CheckMate 743 trial, first-line therapy with nivolumab plus ipilimumab outperformed standard chemotherapy, while in the CONFIRM trial, nivolumab outperformed placebo in patients previously treated with chemotherapy. These two trials represent a major milestone in the treatment of MPM and are set to position immunotherapy as a viable alternative for treatment-naïve patients and patients with progressive disease after chemotherapy.

Dissecting and Reconstructing Matrix in Malignant Mesothelioma Through Histocell-Histochemistry Gradients for Clinical Applications

Background

Malignant pleural mesotheliomas (MM) are known for their heterogenous histology and clinical behavior. MM histology reveals three major tumor cell populations: epithelioid, sarcomatoid, and biphasic. Using a dissecting approach, we showed that histochemical gradients help us better understand tumor heterogeneity and reconsider its histologic classifications. We also showed that this method to characterize MM tumor cell populations provides a better understanding of the underlying mechanisms for invasion and disease progression.

Methods

In a cohort of 87 patients with surgically excised MM, we used hematoxylin and eosin to characterize tumor cell populations and Movat's pentachrome staining to dissect the ECM matrisome. Next, we developed a computerized semi-assisted protocol to quantify and reconstruct the ECM in 3D and examined the clinical association between the matricellular factors and patient outcome.

Results

Epithelioid cells had a higher matrix composition of elastin and fibrin, whereas, in the sarcomatoid type, hyaluronic acid and total collagen were most prevalent. The 3D reconstruction exposed the collagen I and III that form channels surrounding the neoplastic cell blocks. The estimated volume of the two collagen fractions was 14% of the total volume, consistent with the median estimated area of total collagen (12.05 mm2) for epithelioid MM.

Conclusion

Differential patterns in matricellular phenotypes in MM could be used in translational studies to improve patient outcome. More importantly, our data raise the possibility that cancer cells can use the matrisome for disease expansion and could be effectively targeted by anti-collagen, anti-elastin, and/or anti-hyaluronic acid therapies.

Current Management and Future Perspective in Pleural Mesothelioma

Pleural mesothelioma is an aggressive malignancy arising from pleural mesothelial cell lining, predominantly associated with prior exposure to asbestos. The ban on asbestos use has led to its lower incidence in many countries, but globally the disease burden is expected to rise. Therefore, well-planned research is needed to develop more effective, tolerable and affordable drugs. The development of novel treatment has been too slow, with only two regimens of systemic therapy with robust phase 3 data approved formally to date. The treatment scenario for resectable disease remains controversial. However, recent developments in the understanding of disease and clinical trials have been encouraging, and may add better treatment options in the coming years. In this review, we discuss the current treatment options for pleural mesothelioma and shed light on some recent studies and ongoing trials.

G6PD functions as a metabolic checkpoint to regulate granzyme B expression in tumor-specific cytotoxic T lymphocytes

Background

Granzyme B is a key effector of cytotoxic T lymphocytes (CTLs), and its expression level positively correlates with the response of patients with mesothelioma to immune checkpoint inhibitor immunotherapy. Whether metabolic pathways regulate Gzmb expression in CTLs is incompletely understood.

Methods

A tumor-specific CTL and tumor coculture model and a tumor-bearing mouse model were used to determine the role of glucose-6-phosphate dehydrogenase (G6PD) in CTL function and tumor immune evasion. A link between granzyme B expression and patient survival was analyzed in human patients with epithelioid mesothelioma.

Results

Mesothelioma cells alone are sufficient to activate tumor-specific CTLs and to enhance aerobic glycolysis to induce a PD-1^hi Gzmb^lo CTL phenotype. However, inhibition of lactate dehydrogenase A, the key enzyme of the aerobic glycolysis pathway, has no significant effect on tumor-induced CTL activation. Tumor cells induce H3K9me3 deposition at the promoter of G6pd, the gene that encodes the rate-limiting enzyme G6PD in the pentose phosphate pathway, to downregulate G6pd expression in tumor-specific CTLs. G6PD activation increases acetyl-coenzyme A (CoA) production to increase H3K9ac deposition at the Gzmb promoter and to increase Gzmb expression in tumor-specific CTLs converting them from a Gzmb^lo to a Gzmb^hi phenotype, thus increasing CTL tumor lytic activity. Activation of G6PD increases Gzmb⁺ tumor-specific CTLs and suppresses tumor growth in tumor-bearing mice. Consistent with these findings, GZMB expression level was found to correlate with increased survival in patients with epithelioid mesothelioma.

Conclusion

G6PD is a metabolic checkpoint in tumor-activated CTLs. The H3K9me3/G6PD/acetyl-CoA/H3K9ac/Gzmb pathway is particularly important in CTL activation and immune evasion in epithelioid mesothelioma.

The efficacy of immune checkpoint inhibitors in thoracic malignancies

The advent of immune checkpoint inhibitors (ICIs) has rapidly transformed the treatment paradigm for multiple cancer types, including thoracic malignancies. In advanced non-small cell lung cancer (NSCLC), ICIs have shifted treatment paradigm and improved overall survival reaching almost one-third of patients alive at 5 years. ICIs therapies have also modified the therapeutic strategy in first-line setting in metastatic small-cell lung cancer (SCLC) patients as well as in malignant pleural mesothelioma (MPM) improving the overall survival compared with standard treatment. This phenomenon is of huge relevance as both SCLC and MPM were considered orphan diseases without any significant improvement in the therapeutic strategy in the first-line setting during the last 15 years. In this review, we aim to review the efficacy of ICI in thoracic malignancies either in monotherapy or in combination, according to predictive biomarkers, and to the US Food and Drug Administration and the European Medicines Agency approvals of treatment strategies. We address the efficacy of these agents, especially in NSCLC according to PD-L1 expression and histologic subtype.

Immunotherapy, the promise for present and future of malignant pleural mesothelioma (MPM) treatment

Due to occupational asbestosis exposure, the incidence of malignant pleural mesothelioma (MPM) has continuously increased over the last 30 years, with a plateau anticipated around the year 2030 in Western countries. Molecular MPM carcinogenesis involves alterations of NF2, RASSF1, LATS2WT1, p16, as well as BAP-1tumor-suppressor genes, which usually regulate apoptosis, cell invasion, motility, cell division, chromatin remodeling, as well as control of DNA repair. In few selected patients, debulking surgery consisting of pleurectomy-decortication is carried out, resulting in unsatisfactory long-term results. For about 15 years, first-line chemotherapy has been primarily based on a doublet of pemetrexed and cisplatin. Adding the monoclonal antibody bevacizumab (Avastin®), which targets vascular endothelial growth factor (VEGF), has been shown to improve overall survival (OS) by nearly 19 months. The emergence of immune check-point inhibitors (ICIs) in MPM treatment has recently been associated with substantial survival improvements in both second- and first-line settings. Similarly to non-small-cell lung cancer (NSCLC) patients, on-going trials are presently exploring the chemotherapy-ICI combination in MPM management, and depending on their results, this combination could represent a further major advance in this previously orphan disease. The current article reviews recent clinical trial results, as well as future clinical developments in this moving field.

Correlation between immune-related adverse events and therapeutic effects of nivolumab in patients with malignant pleural mesothelioma

Background

Nivolumab is used for the treatment of malignant pleural mesothelioma (MPM). However, immune-related adverse events (irAEs) occur in patients treated with nivolumab. Several studies have reported the correlation between irAEs and therapeutic effects of immune checkpoint inhibitor, but none have reported the correlation in MPM. Here we report a retrospective study which shows the correlation between irAEs and therapeutic effects of nivolumab in patients with MPM.

Methods

This study included patients treated with nivolumab at Tokushima University Hospital from February 2009 to September 2021. We retrospectively reviewed the medical records to evaluate the several clinical factors, such as the presence or absence of irAEs, their severities, progression-free survival (PFS), overall survival (OS) or objective response to the treatment.

Results

Eleven patients received treatment with nivolumab. Objective response rate was 18.2% and the disease control rate was 90.9%. Median PFS was 6.8 months (95% confidence interval, 1.3 to 11.9 months) and median OS was 15.2 months (95% confidence interval, 8.9 to 21.5 months). IrAEs occurred in eight patients (72.7%), and grade ≥ 2 irAEs occurred in six patients (54.5%). PFS and OS were significantly longer in the grade ≥ 2 irAEs group than in grade < 2 irAEs group (median PFS 13.6 vs. 3.8 months, p = 0.0093; median OS not reached vs. 8.6 months, p = 0.0108).

Conclusions

This is the first study to report the correlation between irAEs and therapeutic effects in patients with MPM. Because the presence of irAEs may be associated with a favorable clinical outcome, early detection and appropriate management of irAEs will increase the therapeutic benefits to patients.

Mesothelioma Malignancy and the Microenvironment: Molecular Mechanisms

Several studies have reported that cellular and soluble components of the tumor microenvironment (TME) play a key role in cancer-initiation and progression. Considering the relevance and the complexity of TME in cancer biology, recent research has focused on the investigation of the TME content, in terms of players and informational exchange. Understanding the crosstalk between tumor and non-tumor cells is crucial to design more beneficial anti-cancer therapeutic strategies. Malignant pleural mesothelioma (MPM) is a complex and heterogenous tumor mainly caused by asbestos exposure with few treatment options and low life expectancy after standard therapy. MPM leukocyte infiltration is rich in macrophages. Given the failure of macrophages to eliminate asbestos fibers, these immune cells accumulate in pleural cavity leading to the establishment of a unique inflammatory environment and to the malignant transformation of mesothelial cells. In this inflammatory landscape, stromal and immune cells play a driven role to support tumor development and progression via a bidirectional communication with tumor cells. Characterization of the MPM microenvironment (MPM-ME) may be useful to understand the complexity of mesothelioma biology, such as to identify new molecular druggable targets, with the aim to improve the outcome of the disease. In this review, we summarize the known evidence about the MPM-ME network, including its prognostic and therapeutic relevance.

Matter of TIME: the tumor-immune microenvironment of mesothelioma and implications for checkpoint blockade efficacy

Malignant pleural mesothelioma (MPM) is an incurable cancer with a dismal prognosis and few effective treatment options. Nonetheless, recent positive phase III trial results for immune checkpoint blockade (ICB) in MPM herald a new dawn in the fight to advance effective treatments for this cancer. Tumor mutation burden (TMB) has been widely reported to predict ICB in other cancers, but MPM is considered a low-TMB tumor. Similarly, tumor programmed death-ligand 1 (PD-L1) expression has not been proven predictive in phase III clinical trials in MPM. Consequently, the precise mechanisms that determine response to immunotherapy in this cancer remain unknown. The present review therefore aimed to synthesize our current understanding of the tumor immune microenvironment in MPM and reflects on how specific cellular features might impact immunotherapy responses or lead to resistance. This approach will inform stratified approaches to therapy and advance immunotherapy combinations in MPM to improve clinical outcomes further.

Mesothelioma Risk Score: A New Prognostic Pretreatment, Clinical-Molecular Algorithm for Malignant Pleural Mesothelioma

INTRODUCTION

Prognostic models for malignant pleural mesothelioma have been limited to demographics, symptoms, and laboratory values. We hypothesize higher accuracy using both tumor and patient characteristics. The mesothelioma prognostic test (MPT) and molecular subtype based on claudin-15-to-vimentin expression ratio are molecular signatures associated with survival. Tumor volume (TV) has improved performance compared with clinical staging, whereas neutrophil-to-lymphocyte ratio (NLR) is prognostic for malignant pleural mesothelioma.

METHODS

Tumor specimens and clinical data were collected prospectively from patients who underwent extrapleural pneumonectomy (EPP) or pleurectomy and decortication (PD) during 2007 to 2014. MPT and claudin-15-to-vimentin ratio were determined by real-time quantitative polymerase chain reaction, whereas TV was assessed from preoperative scans. Risk groups were derived from combinations of adverse factors on the basis of the Cox model. Predictive accuracy was assessed using Harrell's c-index.

RESULTS

MPT, molecular subtype, TV, and NLR were independently prognostic in patients with EPP (N = 191), suggesting equal weighting in a final three-group model (c = 0.644). In the PD cohort (N = 193), MPT poor risk combined with TV greater than 200 cm³ was associated with triple the risk compared with other subgroups (hazard ratio = 2.94, 95% confidence interval: 1.70-5.09, p < 0.001) persisting when adjusted for molecular subtype, NLR, performance status, and serum albumin to yield a final three-group model (c = 0.641). The EPP and PD models achieved higher accuracy than published models (c ≤ 0.584, c ≤ 0.575) and pathologic staging (c = 0.554, c = 0.571).

CONCLUSIONS

The novel models use pretreatment parameters obtained from minimally invasive biopsy, imaging, and blood tests to evaluate the expected outcome of each type of surgery in newly diagnosed patients and improve stratification on clinical trials.

Tumor Immune Microenvironment and Genetic Alterations in Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare and fatal disease of the pleural lining. Up to 80% of the MPM cases are linked to asbestos exposure. Even though its use has been banned in the industrialized countries, the cases continue to increase. MPM is a lethal cancer, with very little survival improvements in the last years, mirroring very limited therapeutic advances. Platinum-based chemotherapy in combination with pemetrexed and surgery are the standard of care, but prognosis is still unacceptably poor with median overall survival of approximately 12 months. The genomic landscape of MPM has been widely characterized showing a low mutational burden and the impairment of tumor suppressor genes. Among them, BAP1 and BLM are present as a germline inactivation in a small subset of patients and increases predisposition to tumorigenesis. Other studies have demonstrated a high frequency of mutations in DNA repair genes. Many therapy approaches targeting these alterations have emerged and are under evaluation in the clinic. High-throughput technologies have allowed the detection of more complex molecular events, like chromotripsis and revealed different transcriptional programs for each histological subtype. Transcriptional analysis has also paved the way to the study of tumor-infiltrating cells, thus shedding lights on the crosstalk between tumor cells and the microenvironment. The tumor microenvironment of MPM is indeed crucial for the pathogenesis and outcome of this disease; it is characterized by an inflammatory response to asbestos exposure, involving a variety of chemokines and suppressive immune cells such as M2-like macrophages and regulatory T cells. Another important feature of MPM is the dysregulation of microRNA expression, being frequently linked to cancer development and drug resistance. This review will give a detailed overview of all the above mentioned features of MPM in order to improve the understanding of this disease and the development of new therapeutic strategies.

ERS/ESTS/EACTS/ESTRO guidelines for the management of malignant pleural mesothelioma

The European Respiratory Society (ERS)/European Society of Thoracic Surgeons (ESTS)/European Association for Cardio-Thoracic Surgery (EACTS)/European Society for Radiotherapy and Oncology (ESTRO) task force brought together experts to update previous 2009 ERS/ESTS guidelines on management of malignant pleural mesothelioma (MPM), a rare cancer with globally poor outcome, after a systematic review of the 2009-2018 literature. The evidence was appraised using the Grading of Recommendations, Assessment, Development and Evaluation approach. The evidence syntheses were discussed and recommendations formulated by this multidisciplinary group of experts. Diagnosis: pleural biopsies remain the gold standard to confirm the diagnosis, usually obtained by thoracoscopy but occasionally via image-guided percutaneous needle biopsy in cases of pleural symphysis or poor performance status. Pathology: standard staining procedures are insufficient in ∼10% of cases, justifying the use of specific markers, including BAP-1 and CDKN2A (p16) for the separation of atypical mesothelial proliferation from MPM. Staging: in the absence of a uniform, robust and validated staging system, we advise using the most recent 2016 8th TNM (tumour, node, metastasis) classification, with an algorithm for pretherapeutic assessment. Monitoring: patient's performance status, histological subtype and tumour volume are the main prognostic factors of clinical importance in routine MPM management. Other potential parameters should be recorded at baseline and reported in clinical trials. Treatment: (chemo)therapy has limited efficacy in MPM patients and only selected patients are candidates for radical surgery. New promising targeted therapies, immunotherapies and strategies have been reviewed. Because of limited data on the best combination treatment, we emphasize that patients who are considered candidates for a multimodal approach, including radical surgery, should be treated as part of clinical trials in MPM-dedicated centres.

Immune Microenvironment and Genetics in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare and aggressive malignancy with limited therapeutic options beyond surgery and cytotoxic chemotherapy. The success of immune checkpoint inhibition has been found to correlate with expression of immune-related genes such as CD274 (PD-L1) in lung and other solid cancers. However, only a small subset of MPM patients respond to checkpoint inhibition, and this response has been varied and unpredictable across several clinical trials. Recent advances in next-generation sequencing (NGS) technology have improved our understanding of the molecular features of MPM, also with respect to its genetic signature and how this impacts the immune microenvironment. This article will review current evidence surrounding the interplay between MPM genetics, including epigenetics and transcriptomics, and the immune response.

Pathological Characterization of Tumor Immune Microenvironment (TIME) in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare and highly aggressive disease that arises from pleural mesothelial cells, characterized by a median survival of approximately 13-15 months after diagnosis. The primary cause of this disease is asbestos exposure and the main issues associated with it are late diagnosis and lack of effective therapies. Asbestos-induced cellular damage is associated with the generation of an inflammatory microenvironment that influences and supports tumor growth, possibly in association with patients' genetic predisposition and tumor genomic profile. The chronic inflammatory response to asbestos fibers leads to a unique tumor immune microenvironment (TIME) composed of a heterogeneous mixture of stromal, endothelial, and immune cells, and relative composition and interaction among them is suggested to bear prognostic and therapeutic implications. TIME in MPM is known to be constituted by immunosuppressive cells, such as type 2 tumor-associated macrophages and T regulatory lymphocytes, plus the expression of several immunosuppressive factors, such as tumor-associated PD-L1. Several studies in recent years have contributed to achieve a greater understanding of the pathogenetic mechanisms in tumor development and pathobiology of TIME, that opens the way to new therapeutic strategies. The study of TIME is fundamental in identifying appropriate prognostic and predictive tissue biomarkers. In the present review, we summarize the current knowledge about the pathological characterization of TIME in MPM.

CSF1/CSF1R Axis Blockade Limits Mesothelioma and Enhances Efficiency of Anti-PDL1 Immunotherapy

Simple Summary

CSF1/CSF1R signaling mediates tumor-associated macrophages recruitment and M2 polarization. M2 TAMs are dominant immune populations infiltrating mesothelioma tumors. We evaluated the role of CSF1/CSF1R axis blockade in tumor-infiltrating immune subsets. We also examined the effect of combined anti-CSF1R and anti-PDL1 treatment in mesothelioma progression. We show that CSF1R inhibition impedes mesothelioma progression, abrogates infiltration of TAMs, facilitates an M1 anti-tumor phenotype and activates tumor dendritic and CD8+ T cells. We also show that this inhibitor was able to significantly improve the effectiveness of anti-PDL1 immunotherapy.

Abstract

Colony-Stimulating Factor 1 (CSF1)/Colony-Stimulating Factor Receptor 1 (CSF1R) signaling orchestrates tumor-associated macrophage (TAM) recruitment and polarization towards a pro-tumor M2 phenotype, the dominant phenotype of TAMs infiltrating mesothelioma tumors. We hypothesized that CSF1/CSF1R inhibition would halt mesothelioma growth by targeting immunosuppressive M2 macrophages and unleashing efficient T cell responses. We also hypothesized that CSF1/CSF1R blockade would enhance the efficacy of a PDL1 inhibitor which directly activates CD8+ cells. We tested a clinically relevant CSF1R inhibitor (BLZ945) in mesothelioma treatment using syngeneic murine models. We evaluated the role of CSF1/CSF1R axis blockade in tumor-infiltrating immune subsets. We examined the effect of combined anti-CSF1R and anti-PDL1 treatment in mesothelioma progression. CSF1R inhibition impedes mesothelioma progression, abrogates infiltration of TAMs, facilitates an M1 anti-tumor phenotype and activates tumor dendritic and CD8+ T cells. CSF1R inhibition triggers a compensatory PD-1/PDL1 upregulation in tumor and immune cells. Combined CSF1R inhibitor with an anti-PDL1 agent was more effective in retarding mesothelioma growth compared to each monotherapy. In experimental mesotheliomas, CSF1R inhibition abrogates tumor progression by limiting suppressive myeloid populations and enhancing CD8+ cell activation and acts synergistically with anti-PDL1.

Immune checkpoint inhibitors for unresectable malignant pleural mesothelioma

Unresectable malignant pleural mesothelioma (MPM) is an aggressive disease with a 5-year survival rate of approximately 10%. Recent data suggest that MPM is an immunologically active tumor, in which checkpoint inhibition through the blockade of the anti-cytotoxic T lymphocyte antigen-4 (-CTLA-4) or anti-programmed cell death 1 (PD-1) could play a major therapeutic role. Initially, clinical trials evaluated immune checkpoint inhibitors (ICIs) in the salvage setting after platinum-based chemotherapy with mixed results in terms of efficacy. More recently, the combination of the anti-CTLA-4 agent ipilimumab plus the anti-PD-1 agent nivolumab was tested in the front-line setting, and reported a superior survival as compared to platinum/pemetrexed. While other clinical trials ore ongoing in order to investigate ICIs for MPM, it seems now evident that we have entered a new "era" for the treatment of MPM. In the future, a few issues need to be solved with regard to the use of ICIs for MPM. Among them, there is the identification of biomarkers of sensitivity to immunotherapy that may help enrich the patient population who could benefit the most from treatment, while avoiding for some other patients the potential occurrence of immune-related side effects from therapies that are anticipated to be ineffective.

Prognostic impact of PD-1 and PD-L1 expression in malignant pleural mesothelioma: an international multicenter study

BACKGROUND

Programmed cell death 1/programmed death ligand 1 (PD-1/PD-L1) immune-checkpoint blockade is a promising new therapeutic strategy in cancer. However, expression patterns and prognostic significance of PD-L1 and PD-1 are still controversial in human malignant pleural mesothelioma (MPM).

METHODS

Formalin-fixed paraffin-embedded (FFPE) tumor samples from 203 MPM patients receiving standard treatment without immunotherapy were collected from 5 European centers. PD-L1 and PD-1 expression of tumor cells (TCs) and tumor-infiltrating lymphocytes (TILs) were measured by immunohistochemistry and correlated with clinical parameters and long-term outcome.

RESULTS

High (>10%) PD-L1 TC and PD-1 TILs expressions were found in 18 (8%) and 39 (24%) patients, respectively. PD-L1 was rarely expressed by TILs [≥1%, n=13 (8%); >10%, n=1]. No significant associations were found between the PD-L1 or PD-1 expression of TCs or TILs and clinicopathological parameters such as stage or histological subtype. Notably, patients with high (>10%) TC-specific PD-L1 expression exhibited significantly worse median overall survival (OS) (6.3 vs. 15.1 months of those with low TC PD-L1 expression; HR: 2.51, P<0.001). In multivariate cox regression analysis adjusted for clinical parameters, high TC PD-L1 expression (>10%) proved to be an independent negative prognostic factor for OS (HR: 2.486, P=0.005). There was no significant correlation between PD-L1 or PD-1 expression of TILs and OS.

CONCLUSIONS

In this multicenter cohort study, we demonstrate that high (>10%) PD-L1 expression of TCs independently predicts worse OS in MPM. Further studies are warranted to investigate the value of PD-L1/PD-1 expression as a marker for treatment response in MPM patients receiving immunotherapy.

Transcriptional perturbation of protein arginine methyltransferase-5 exhibits MTAP-selective oncosuppression

We hypothesized that small molecule transcriptional perturbation could be harnessed to target a cellular dependency involving protein arginine methyltransferase 5 (PRMT5) in the context of methylthioadenosine phosphorylase (MTAP) deletion, seen frequently in malignant pleural mesothelioma (MPM). Here we show, that MTAP deletion is negatively prognostic in MPM. In vitro, the off-patent antibiotic Quinacrine efficiently suppressed PRMT5 transcription, causing chromatin remodelling with reduced global histone H4 symmetrical demethylation. Quinacrine phenocopied PRMT5 RNA interference and small molecule PRMT5 inhibition, reducing clonogenicity in an MTAP-dependent manner. This activity required a functional PRMT5 methyltransferase as MTAP negative cells were rescued by exogenous wild type PRMT5, but not a PRMT5E444Q methyltransferase-dead mutant. We identified c-jun as an essential PRMT5 transcription factor and a probable target for Quinacrine. Our results therefore suggest that small molecule-based transcriptional perturbation of PRMT5 can leverage a mutation-selective vulnerability, that is therapeutically tractable, and has relevance to 9p21 deleted cancers including MPM.

Pathology of Malignant Pleural Mesothelioma

Despite multiple diagnostic toolkits, the diagnosis of diffuse malignant pleural mesothelioma relies primarily on proper histologic assessment. The definitive diagnosis of diffuse malignant pleural mesothelioma is based on the pathologic assessment of tumor tissue, which can be obtained from core biopsy sampling, pleurectomy, or other more extensive resections, such as extrapleural pneumonectomy. Given its rarity and overlapping microscopic features with other conditions, the histologic diagnosis of diffuse malignant pleural mesothelioma is challenging. This review discusses the pathologic features and the differential diagnosis of diffuse malignant pleural mesothelioma, including select diagnostic pitfalls.

Programmed cell death 1 ligand 1 (PD-L1) expression is associated with poor prognosis of malignant pleural mesothelioma patients with good performance status

Malignant pleural mesothelioma (MPM) is often associated with a poor prognosis and options for the treatment of this disease are few. To date, the important role of the immune microenvironment in modifying the disease natural history is well established. The programmed cell death pathway (PD-1/PD-L1) limits the T lymphocyte activation in peripheral tissues when an inflammatory response occurs, and controls the tumour immune escape. PD-L1 is broadly expressed in several malignant tumours and associated with poor clinical outcomes. Thus, the aim of our study is to investigate the potential role of PD-L1 expression in MPM prognosis. Biopsy samples from 198 patients diagnosed with MPM were examined by immunohistochemistry (IHC) and reverse transcription-polymerase chain reaction (RT-PCR) to evaluate PD-L1 protein and gene expression. For PD-L1 protein expression we consider at least 5% membranous staining as positive. Gene expression levels were calculated with ΔΔCt method. Positive expression of PD-L1 by IHC was correlated with worse overall survival (OS; p=0.0225) in MPM patients. PD-L1 positive status was correlated with worse OS in the subgroup of patients with ECOG score <2 (p=0.0004, n=129) and these data were confirmed by multivariate analysis. No significant correlation was found between PD-L1 gene expression and OS. Our results show that PD-L1 evaluated by IHC assay may be a prognostic biomarker for MPM patients with good performance status.

BCL-XL is an actionable target for treatment of malignant pleural mesothelioma

Despite having one of the lowest survival rates of all cancers, there have been no new approved treatments for malignant pleural mesothelioma (MPM) in over a decade. Standard-of-care treatment relies on Cisplatin plus Pemetrexed chemotherapy. Here, we tested a suite of BH3-mimetic drugs targeting BCL-2 pro-survival proteins of the intrinsic apoptotic pathway. We found BCL-XL is the dominant pro-survival protein in a panel of cell lines in vitro, though potent, synergistic cell killing occurred with MCL-1 co-targeting. This correlates with high-level expression of BCL-XL and MCL-1 in cell lines and a large cohort of patient tumour samples. BCL-XL inhibition combined with Cisplatin also enhanced cell killing. In vivo BCL-XL inhibition was as effective as Cisplatin, and the combination enhanced tumour growth control and survival. Genetic ablation of MCL-1 also enhanced the effects of BCL-XL inhibitors, in vivo. Combined, these data provide a compelling rationale for the clinical investigation of BH3-mimetics targeting BCL-XL in MPM.

Expression status of PD-L1 and B7-H3 in mesothelioma

Mesothelioma is a rare, aggressive malignancy with poor outcome, and has limited treatment options. The aim of this study was to perform a comprehensive analysis of programmed death ligand 1 (PD-L1) and B7 homolog 3 (B7-H3) expression in mesothelioma. We investigated the protein expression of PD-L1 and B7-H3 and their potential correlation with histological subtype, which might help to develop new therapies targeting these immune checkpoint molecules. Expression analysis of PD-L1 and B7-H3 was performed by immunohistochemistry using serial tissue sections of specimens obtained from 31 patients with mesothelioma. Tumors were classified into 22 epithelioid, 6 sarcomatoid, and 3 biphasic types. Of the 31 patients, 13 (41.9%) were positive for PD-L1 and 28 (90.3%) were B7-H3 positive. Twelve of the 13 PD-L1 positive patients were positive for B7-H3. PD-L1 and B7-H3 were widely co-expressed in biphasic and sarcomatoid type tumor cells. These findings might provide a rationale for the use of combination therapy for mesothelioma by targeting PD-L1 and B7-H3, as well as the development of anti-B7-H3 or anti-PD-L1 single agents.

Characterization of the immune microenvironment in malignant pleural mesothelioma reveals prognostic subgroups of patients

Malignant pleural mesothelioma (MPM) is a rare tumor with an extremely poor prognosis. Its pathogenesis is related to an immune response against asbestos fibers. The T-lymphocytes, including CD8^POS and CD4^POS cells, are an important part of the MPM immune microenvironment, and likely contribute to the therapy resistance observed in these tumors. Here, we sought to characterize the MPM-specific lymphocytes subpopulations within the tumor immune microenvironment to identify novel clinically relevant immunologic subtypes of tumors. Representative formalin-fixed, paraffin-embedded (FFPE) tissue blocks of 88 MPMs were included in tissue microarrays and subjected to tumor-infiltrating lymphocytes (TILs) quantification and subtyping by immunohistochemistry (IHC) with antibodies specific for CD4, CD8, and CD19. Further, PD-L1 (clone 22C3) expression was assessed by IHC as a combined positive score (CPS). Our data show that PD-L1 expression by tumor cells or the presence of a sarcomatoid component is related to increased stromal TILs presence in MPM. Survival analyses showed that low CD4^POS and high CD8^POS stromal TILs are associated with poor patients' survival. In MPMs with PD-L1 CPS > 1, stromal CD8^HIGH was a poor prognostic factor, akin stromal CD4^POS peritumoral TILs correlated with a worse prognosis. Furthermore, we demonstrated that a high CD4^POS/CD8^POS ratio in the tumor immune microenvironment is an independent prognostic factor for survival. Finally, we provided evidence that the characterization of the stromal immune landscape of MPM predicts responses to chemotherapy in subgroups of MPM. The results of this study provide novel insights into the clinical scenario of immune-related biomarkers in MPM.

PD-L1 and prognosis in patients with malignant pleural mesothelioma: a meta-analysis and bioinformatics study

Background

The prognostic value of programmed death-ligand 1 (PD-L1) expression in patients with malignant pleural mesothelioma (MPM) has been controversial according to previous investigations. Therefore, we conducted a meta-analysis to assess the potential prognostic significance of PD-L1 expression in MPM.

Methods

PubMed, Embase, Web of Science, Scopus, and the Cochrane Library were thoroughly searched for relevant original articles published before 9 April 2020. The pooled hazard ratios (HRs) and 95% confidence intervals (CIs) of overall survival (OS) and progression-free survival (PFS) were calculated. The results of the meta-analysis were verified using The Cancer Genome Atlas (TCGA) dataset.

Results

In total 16 studies were included in our meta-analysis. A high PD-L1 expression was associated with a poor OS (HR = 1.53, 95% CI = 1.28-1.83, p < 0.001), but not a grave PFS (HR = 1.07, 95% CI = 0.82-1.39, p = 0.643) in MPM. Furthermore, the PD-L1 expression correlated with the sarcomatoid + biphasic type of MPM (odds ratio = 4.32, 95% CI = 2.16-8.64, p < 0.001). TCGA data indicated that PD-L1 was a significant prognostic factor for OS (HR = 2.069, 95% CI = 1.136-3.769, p = 0.0175), but not for PFS (HR = 1.205, 95% CI = 0.572-2.539, p = 0.624), which was in accordance with the results of the meta-analysis.

Conclusion

A high PD-L1 expression is a significant prognostic factor for poor OS of patients with MPM. We therefore suggest that PD-L1 expression levels can be used to predict the clinical outcomes of patients with MPM in the future.

Trabectedin in Malignant Pleural Mesothelioma: Results From the Multicentre, Single Arm, Phase II ATREUS Study

INTRODUCTION

New therapeutic approaches in unresectable malignant pleural mesothelioma (MPM) are eagerly awaited. Trabectedin is an antitumor agent with an effect on cancer cell proliferation and a modulating action on tumor microenvironment. The ATREUS study explored the activity and safety of trabectedin in patients with unresectable MPM.

METHODS

Epithelioid patients with MPM received trabectedin as second-line while biphasic/sarcomatoid patients with MPM as first- or second-line therapy. Treatment was given intravenously at an initially planned dose of 1.3 mg/m² every 3 weeks, until progression or unacceptable toxicity. The primary endpoint was progression-free survival rate at 12 weeks (PFS_12wks).

RESULTS

Overall, 78 patients (54%) had epithelioid and 67 (46%) nonepithelioid MPM. PFS_12wks in 62 evaluable patients with epithelioid MPM was 43.5% (80% confidence interval 34.9%-52.5%); median progression-free and overall survival were 2.4 and 9.0 months, respectively. PFS_12wks in 52 evaluable patients with nonepithelioid MPM was 30.8% (90% confidence interval 20.3%-42.9%); median progression-free and overall survival were 1.7 and 5.4 months. Trabectedin starting dose was amended due to excess of liver toxicity. Eighty-four (64%) and 48 (36%) patients received 1.3 mg/m² and 1.1. mg/m², respectively. The most common grade 3-4 toxicities were hepatotoxicity, leukopenia/neutropenia, and fatigue. Grade 3-4 hepatotoxicity was reported in 59 (70%) patients treated at 1.3 mg/m², and in 19 (40%) treated at 1.1 mg/m².

CONCLUSIONS

Trabectedin showed modest clinical activity, at the expense of relevant liver toxicity. Further development of this drug in MPM at full doses is not warranted.

ERS/ESTS/EACTS/ESTRO guidelines for the management of malignant pleural mesothelioma

The European Respiratory Society (ERS)/European Society of Thoracic Surgeons (ESTS)/European Association for Cardio-Thoracic Surgery (EACTS)/European Society for Radiotherapy and Oncology (ESTRO) task force brought together experts to update previous 2009 ERS/ESTS guidelines on management of malignant pleural mesothelioma (MPM), a rare cancer with globally poor outcome, after a systematic review of the 2009-2018 literature. The evidence was appraised using the Grading of Recommendations, Assessment, Development and Evaluation approach. The evidence syntheses were discussed and recommendations formulated by this multidisciplinary group of experts. Diagnosis: pleural biopsies remain the gold standard to confirm the diagnosis, usually obtained by thoracoscopy but occasionally via image-guided percutaneous needle biopsy in cases of pleural symphysis or poor performance status. Pathology: standard staining procedures are insufficient in ∼10% of cases, justifying the use of specific markers, including BAP-1 and CDKN2A (p16) for the separation of atypical mesothelial proliferation from MPM. Staging: in the absence of a uniform, robust and validated staging system, we advise using the most recent 2016 8th TNM (tumour, node, metastasis) classification, with an algorithm for pre-therapeutic assessment. Monitoring: patient's performance status, histological subtype and tumour volume are the main prognostic factors of clinical importance in routine MPM management. Other potential parameters should be recorded at baseline and reported in clinical trials. Treatment: (chemo)therapy has limited efficacy in MPM patients and only selected patients are candidates for radical surgery. New promising targeted therapies, immunotherapies and strategies have been reviewed. Because of limited data on the best combination treatment, we emphasise that patients who are considered candidates for a multimodal approach, including radical surgery, should be treated as part of clinical trials in MPM-dedicated centres.

Clinical significance of histologic subtyping of malignant pleural mesothelioma

Malignant mesothelioma (MM) is uncommon, but very aggressive tumor arising from the mesothelial cells of pleura, pericardium, peritoneum, and tunica vaginalis. Despite multimodality treatments 5-year survival is only 5% after the diagnosis. Histology and TNM staging system are still the best prognostic factors. Furthermore, histologic subtype of MM determines the clinical management of the patients. According to the 2015 WHO classification, MM is divided into diffuse, localized and well differentiated papillary mesothelioma. Major histologic subtypes of diffuse MM, namely epithelioid, biphasic and sarcomatoid, have different prognosis. However, in the last decade it has become evident that more detailed subclassification and histologic/cytological characterization of MM have prognostic and perhaps predictive implications. In this review, major histologic subtypes and cytological features of MM are presented and their relation with prognosis and predictive biomarkers is discussed.

Preliminary study highlights the potential of immune checkpoint inhibitors in sarcomatoid mesothelioma

Background

Malignant pleural mesothelioma (MPM) is well known as an aggressive disease with poor survival. This has sparked trials of alternate immune-based therapies in MPM. While up to a quarter of MPM patients respond to immune checkpoint inhibitors (ICIs), predicting response remains challenging and PD-L1 expression alone has been deemed insufficient. Additionally, patients with sarcomatoid MPM are often excluded from trials utilizing ICIs due to their rapid progression. Here, we analyze the association of T lymphocytes with response to ICI-based immunotherapy to uncover predictive immune markers across subtypes.

Methods

Retrospective analysis of immunotherapy treated mesothelioma patient cohorts from two sites were pooled. Patient characteristics, including age, sex, subtype and previous treatment were captured. Multiplex immunohistochemistry was used to assess proportions of CD4, CD8, CD45RO and FOXP3 positive infiltrates in MPM and their association with progression free (PFS) and overall (OS) survival post immunotherapy.

Results

Samples derived from 22 patients were analyzed; 13 (59%) had epithelioid MPM, 6 (27%) sarcomatoid and 3 (14%) biphasic. The overall ICI response rate was 40%, with a median PFS (mPFS) and OS (mOS) of 3.8 and 11.17 months, respectively. Of the subtypes, sarcomatoid patients displayed the greatest median PFS and OS (>28 months) post ICI compared to the epithelioid subtype (3 and 11 months respectively), which correlated with higher proportions of infiltrating CD8⁺, CD45RO⁺ and CD8⁺CD45RO⁺ cells. Patients who received ICIs as first-line therapy had greater PFS than those who received it as second or third line post-chemotherapy.

Conclusions

High proportions of T lymphocytes and CD45RO⁺ cells were associated with prolonged mPFS and mOS in sarcomatoid patients treated with ICI immunotherapy. These data support the expansion of trials utilizing single and combination ICIs as first-line therapy in sarcomatoid MPM and warrants further studies testing the impact or detriment of chemotherapy pre-ICI.

Immune Checkpoint Inhibitors in Thoracic Malignancies: Review of the Existing Evidence by an IASLC Expert Panel and Recommendations

In the past 10 years, a deeper understanding of the immune landscape of cancers, including immune evasion processes, has allowed the development of a new class of agents. The reactivation of host antitumor immune response offers the potential for long-term survival benefit in a portion of patients with thoracic malignancies. The advent of programmed cell death protein 1/programmed death ligand-1 immune checkpoint inhibitors (ICIs), both as single agents and in combination with chemotherapy, and more recently, the combination of ICI, anti-programmed cell death protein 1, and anticytotoxic T-lymphocyte antigen 4 antibody, have led to breakthrough therapeutic advances for patients with advanced NSCLC, and to a lesser extent, patients with SCLC. Encouraging activity has recently emerged in pretreated patients with thymic carcinoma (TC). Conversely, in malignant pleural mesothelioma, pivotal positive signs of activity have not been fully confirmed in randomized trials. The additive effects of chemoradiation and immunotherapy suggested intriguing potential for therapeutic synergy with combination strategies. This has led to the introduction of ICI consolidation therapy in stage III NSCLC, creating a platform for future therapeutic developments in earlier-stage disease. Despite the definitive clinical benefit observed with ICI, primary and acquired resistance represent well-known biological phenomena, which may affect the therapeutic efficacy of these agents. The development of innovative strategies to overcome ICI resistance, standardization of new patterns of ICI progression, identification of predictive biomarkers of response, optimal treatment duration, and characterization of ICI efficacy in special populations, represent crucial issues to be adequately addressed, with the aim of improving the therapeutic benefit of ICI in patients with thoracic malignancies. In this article, an international panel of experts in the field of thoracic malignancies discussed these topics, evaluating currently available scientific evidence, with the final aim of providing clinical recommendations, which may guide oncologists in their current practice and elucidate future treatment strategies and research priorities.

Combined MEK and PI3K/p110β Inhibition as a Novel Targeted Therapy for Malignant Mesothelioma Displaying Sarcomatoid Features

Among malignant mesotheliomas (MM), the sarcomatoid subtype is associated with higher chemoresistance and worst survival. Due to its low incidence, there has been little progress in the knowledge of the molecular mechanisms associated with sarcomatoid MM, which might help to define novel therapeutic targets. In this work, we show that loss of PTEN expression is frequent in human sarcomatoid MM and PTEN expression levels are lower in sarcomatoid MM than in the biphasic and epithelioid subtypes. Combined Pten and Trp53 deletion in mouse mesothelium led to nonepithelioid MM development. In Pten;Trp53-null mice developing MM, the Gαi2-coupled receptor subunit activated MEK/ERK and PI3K, resulting in aggressive, immune-suppressed tumors. Combined inhibition of MEK and p110β/PI3K reduced mouse tumor cell growth in vitro. Therapeutic inhibition of MEK and p110β/PI3K using selumetinib (AZD6244, ARRY-142886) and AZD8186, two drugs that are currently in clinical trials, increased the survival of Pten;Trp53-null mice without major toxicity. This drug combination effectively reduced the proliferation of primary cultures of human pleural (Pl) MM, implicating nonepithelioid histology and high vimentin, AKT1/2, and Gαi2 expression levels as predictive markers of response to combined MEK and p110β/PI3K inhibition. Our findings provide a rationale for the use of selumetinib and AZD8186 in patients with MM with sarcomatoid features. This constitutes a novel targeted therapy for a poor prognosis and frequently chemoresistant group of patients with MM, for whom therapeutic options are currently lacking. SIGNIFICANCE: Mesothelioma is highly aggressive; its sarcomatoid variants have worse prognosis. Building on a genetic mouse model, a novel combination therapy is uncovered that is relevant to human tumors.

Efficacy and Safety of Avelumab Treatment in Patients With Advanced Unresectable Mesothelioma: Phase 1b Results From the JAVELIN Solid Tumor Trial

Importance

Patients with malignant mesothelioma whose disease has progressed after platinum and pemetrexed treatment have limited options. Anti-programmed cell death 1 (PD-1) antibodies have antitumor activity in this disease, but little is known about the activity of anti-programmed cell death ligand 1 (PD-L1) antibodies in patients with mesothelioma.

Objective

To assess the efficacy and safety of avelumab in a cohort of patients with previously treated mesothelioma.

Design, Setting, and Participants

Phase 1b open-label study (JAVELIN Solid Tumor) in patients with unresectable mesothelioma that progressed after platinum and pemetrexed treatment, enrolled at 25 sites in 3 countries between September 9, 2014, and July 22, 2015.

Interventions

Participants received avelumab, 10 mg/kg, every 2 weeks until disease progression, unacceptable toxic effects, or withdrawal from the study.

Main Outcomes and Measures

Prespecified end points included confirmed best overall response based on Response Evaluation Criteria In Solid Tumors, version 1.1; duration of response; progression-free survival (PFS); overall survival (OS); PD-L1 expression-based analyses; and safety.

Results

Of 53 patients treated with avelumab, the median age was 67 (range, 32-84) years; 32 (60%) were male. As of December 31, 2016, median follow-up was 24.8 (range, 16.8-27.8) months. Twenty patients (38%) had 3 or more previous lines of therapy (median, 2; range, 1-8). The confirmed objective response rate (ORR) was 9% (5 patients; 95% CI, 3.1%-20.7%), with complete response in 1 patient and partial response in 4 patients. Responses were durable (median, 15.2 months; 95% CI, 11.1 to not estimable months) and occurred in patients with PD-L1-positive tumors (3 of 16; ORR, 19%; 95% CI, 4.0%-45.6%) and PD-L1-negative tumors (2 of 27; ORR, 7%; 95% CI, 0.9%-24.3%) based on a 5% or greater PD-L1 cutoff. Disease control rate was 58% (31 patients). Median PFS was 4.1 (95% CI, 1.4-6.2) months, and the 12-month PFS rate was 17.4% (95% CI, 7.7%-30.4%). Median OS was 10.7 (95% CI, 6.4-20.2) months, and the median 12-month OS rate was 43.8% (95% CI, 29.8%-57.0%). Five patients (9%) had a grade 3 or 4 treatment-related adverse event, and 3 (6%) had a grade 3 or 4 immune-related, treatment-related adverse event. There were no treatment-related deaths.

Conclusions and Relevance

Avelumab showed durable antitumor activity and disease control with an acceptable safety profile in a heavily pretreated cohort of patients with mesothelioma.

Trial Registration

ClinicalTrials.gov identifier: NCT01772004.

Prognostic influence of tumor microenvironment after hypofractionated radiation and surgery for mesothelioma

OBJECTIVE

Cytotoxic CD8+ tumor infiltrating lymphocytes (TILs) can contribute to the benefit of hypofractionated radiation, but programmed cell death pathways (programmed cell death 1 and programmed cell death ligand 1 [PD-1/PD-L1]) may provide a mechanism of tumor immune escape. We therefore reviewed the influence of PD-1/PD-L1 and CD8+ TILs on survival after accelerated hypofractionated hemithoracic radiation followed by extrapleural pneumonectomy for malignant pleural mesothelioma (MPM).

METHODS

Sixty-nine consecutive patients undergoing the protocol of Surgery for Mesothelioma after Radiation Therapy (SMART) between November 2008 and February 2016 were analyzed for the presence of PD-L1 on tumor cells, PD-1 on inflammatory cells, and CD8+ TILs. Comparison was made with a cohort of patients undergoing extrapleural pneumonectomy after induction chemotherapy (n = 14) and no induction (n = 2) between March 2005 and October 2008. PD-L1 expression on tumor cells ≥1% was considered positive. CD8+ TILs and PD-1 expression were scored as a percentage of positive cells.

RESULTS

PD-L1 was negative in 75% of MPM after completion of SMART. CD8+ TILs ranged between 0.24% and 8.47% (median 2%). CD8+ TILs ≥2% was associated with significantly better survival in epithelioid MPM (median survival 3.7 years vs 2.3 years in CD8+ TILs <2%; P = .02). PD-L1 positivity was associated with worse survival in biphasic MPM (median survival, 0.4 years vs 1.5 years in biphasic PD-L1 negative tumors; P = .07) after SMART. Multivariate analysis demonstrated that epithelioid MPM, nodal disease, and CD8+ TILs were independent predictors of survival after SMART.

CONCLUSIONS

The influence of tumor microenvironment on survival differs between epithelioid and nonepithelioid MPM. CD8+ TILs is an independent factor associated with better survival in epithelioid MPM treated with SMART.

Approved and emerging treatments of malignant pleural mesothelioma in elderly patients

Introduction: Malignant pleural mesothelioma (MPM) is a rare neoplasm with asbestos exposure as the dominant etiologic agent. Owing to the long latent period following exposure, MPM is often diagnosed late in life. Despite this, elderly patients are under-represented in clinical trials. To date, data regarding the tolerability and efficacy of anticancer treatments for elderly patients affected by MPM are still lacking.Areas covered: The current state-of-the-art of approved treatments employed in the treatment of MPM elderly patients is reviewed and discussed, with a look to emerging therapies. A structured search of bibliographic databases for peer-reviewed research literature and of main meeting abstracts using a focused review question was undertaken.Expert opinion: Even though the median age of MPM patients enrolled in the most recent experimental trials is increasing, no specific analysis has been reported so far in the elderly. Moreover, no data are available for the 'oldest of the elderly' (>75 years). Treatment of elderly patients with MPM is one of the major challenges to the clinician. There is a clear need of large, well-conducted retrospective studies and above all of prospective investigations in this patient population, both in the first-and in the second-line setting.

Redefining malignant pleural mesothelioma types as a continuum uncovers immune-vascular interactions

BACKGROUND

Malignant Pleural Mesothelioma (MPM) is an aggressive disease related to asbestos exposure, with no effective therapeutic options.

METHODS

We undertook unsupervised analyses of RNA-sequencing data of 284 MPMs, with no assumption of discreteness. Using immunohistochemistry, we performed an orthogonal validation on a subset of 103 samples and a biological replication in an independent series of 77 samples.

FINDINGS

A continuum of molecular profiles explained the prognosis of the disease better than any discrete model. The immune and vascular pathways were the major sources of molecular variation, with strong differences in the expression of immune checkpoints and pro-angiogenic genes; the extrema of this continuum had specific molecular profiles: a "hot" bad-prognosis profile, with high lymphocyte infiltration and high expression of immune checkpoints and pro-angiogenic genes; a "cold" bad-prognosis profile, with low lymphocyte infiltration and high expression of pro-angiogenic genes; and a "VEGFR2+/VISTA+" better-prognosis profile, with high expression of immune checkpoint VISTA and pro-angiogenic gene VEGFR2. We validated the gene expression levels at the protein level for a subset of five selected genes belonging to the immune and vascular pathways (CD8A, PDL1, VEGFR3, VEGFR2, and VISTA), in the validation series, and replicated the molecular profiles as well as their prognostic value in the replication series.

INTERPRETATION

The prognosis of MPM is best explained by a continuous model, which extremes show specific expression patterns of genes involved in angiogenesis and immune response.

Use of Programmed Death Ligand-1 (PD-L1) Staining to Separate Sarcomatoid Malignant Mesotheliomas From Benign Mesothelial Reactions

CONTEXT.—

The separation of benign from malignant mesothelial proliferations is a difficult morphologic problem. Some mesotheliomas stain for programmed death ligand-1 (PD-L1).

OBJECTIVE.—

To determine whether PD-L1 staining can separate mesotheliomas from reactive mesothelial proliferations (RMPs).

DESIGN.—

We stained 2 tissue microarrays containing in toto 62 malignant mesotheliomas and 88 RMPs, using anti-PD-L1 antibody 22C3. Staining was graded by using an immunoreactive score encompassing intensity/distribution and was divided into negative, weak, moderate, and strong. Because PD-L1 staining can be heterogeneous, we also stained 10 whole sections of sarcomatoid/desmoplastic mesotheliomas (SMMs) and 10 whole sections of spindled RMPs in the form of organizing pleuritis, the major morphologic differential of SMM. These 20 cases were not on the tissue microarrays.

RESULTS.—

RMPs showed generally negative, or occasionally weak staining in either the epithelioid or spindle cell compartments, whereas moderate to strong staining was seen in 10 of 14 SMMs but only in 6 of 48 epithelioid mesotheliomas (EMMs). The difference between SMM and RMP staining was statistically significant (P < .001), but between EMM and RMP was not significant. Whole section cases of organizing pleuritis showed no staining (N = 8) or weak staining (N = 2), whereas moderate/strong staining was seen in 9 of 10 whole sections of SMMs, a statistically significant difference (P = .02). There were no "hot spots" of RMP staining, suggesting that heterogeneous staining of RMPs is not a confounder.

CONCLUSIONS.—

Strong diffuse PD-L1 staining using antibody 22C3 supports a diagnosis of SMM when the differential diagnosis is RMPs, but PD-L1 staining is not useful for separating EMMs from RMPs.

Immune checkpoint inhibition for the treatment of mesothelioma

INTRODUCTION

Combination chemotherapy is currently standard care for advanced mesothelioma. Checkpoint blockade is a promising new treatment.

AREAS COVERED

This review covers clinical use and biomarkers of checkpoint blockade. Medline search used keywords 'mesothelioma' combined with 'checkpoint blockade' OR 'PD-L1' OR 'PD1' OR 'anti-CTLA4'; the search terms AND 'clinical trial' or AND 'biomarker*' were added. Handsearching covered abstracts from relevant meetings from 2016 to 2018 and reference lists. Data informed a narrative review.

EXPERT OPINION

Single agent anti-CTLA4 blockade is inactive in mesothelioma. Single agent PD-1 blockade as second or subsequent treatment gives 20-29% partial responses; no randomized comparisons against placebo or chemotherapy are available. Biomarkers of response have been difficult to identify. There is no consensus as to whether tumor PD-L1 expression predicts outcomes. Combination checkpoint inhibitors (CTLA4 and PD1 blockade) provide a small incremental increase in response rates and progression-free survival. Chemoimmunotherapy is the next frontier.