Prognostic Role of Soluble and Extracellular Vesicle-Associated PD-L1, B7-H3 and B7-H4 in Non-Small Cell Lung Cancer Patients Treated with Immune Checkpoint Inhibitors.

The treatment of non-small cell lung cancer (NSCLC) has changed dramatically with the advent of immune checkpoint inhibitors (ICIs). Despite encouraging results, their efficacy remains limited to a subgroup of patients. Circulating immune checkpoints in soluble (s) form and associated with extracellular vesicles (EVs) represent promising markers, especially in ICI-based therapeutic settings. We evaluated the prognostic role of PD-L1 and of two B7 family members (B7-H3, B7-H4), both soluble and EV-associated, in a cohort of advanced NSCLC patients treated with first- (n = 56) or second-line (n = 126) ICIs. In treatment-naïve patients, high baseline concentrations of sPD-L1 (>24.2 pg/mL) were linked to worse survival, whereas high levels of sB7-H3 (>0.5 ng/mL) and sB7-H4 (>63.9 pg/mL) were associated with better outcomes. EV characterization confirmed the presence of EVs positive for PD-L1 and B7-H3, while only a small portion of EVs expressed B7-H4. The comparison between biomarker levels at the baseline and in the first radiological assessment under ICI-based treatment showed a significant decrease in EV-PD-L1 and an increase in EV-B7H3 in patients in the disease response to ICIs. Our study shows that sPD-L1, sB7-H3 and sB7-H4 levels are emerging prognostic markers in patients with advanced NSCLC treated with ICIs and suggests potential EV involvement in the disease response to ICIs.

Immune Checkpoint Blockade: A Strategy to Unleash the Potential of Natural Killer Cells in the Anti-Cancer Therapy.

Immune checkpoint inhibitors (ICIs) immunotherapy has represented a breakthrough in cancer treatment. Clinical use of ICIs has shown an acceptable safety profile and promising antitumor activity. Nevertheless, some patients do not obtain clinical benefits after ICIs therapy. In order to improve and cure an increasing number of patients, the field has moved toward the discovery of new ICIs expressed by cells of innate immunity with an elevated inherent antitumor activity, such as natural killer cells. This review will focus on the recent findings concerning the role of classical and non-classical immune checkpoint molecules and receptors that regulate natural killer cell function, as potential targets, and their future clinical application.

Immunotherapy-chemotherapy combinations for non-small cell lung cancer: current trends and future perspectives.

INTRODUCTION: In recent years, immunotherapy has become a pillar in the treatment of advanced, non-oncogene-addicted non-small cell lung cancer (NSCLC). Programmed death ligand 1 (PD-L1) expression is currently the only factor used to predict response to immunotherapy in clinical practice. Specifically, single-agent pembrolizumab as first-line therapy is approved for tumors with high expression of PD-L1 (≥50%) while immunotherapy and chemotherapy are approved for any PD-L1. However, combinations of immune-checkpoint inhibitors (ICIs) and other agents may confer higher benefit than immunotherapy alone in some circumstances. AREAS COVERED: We reviewed the available data regarding the combined use of ICIs and chemotherapy in patients with advanced, treatment-naïve NSCLC. In light of the benefit demonstrated in advanced disease, these combinations have been subsequently tested in other settings. We collected the most relevant findings regarding efficacy and safety of chemo-immunotherapy combinations in early and locally advanced NSCLC. EXPERT OPINION: Immune-chemotherapy combinations demonstrated benefit in the advanced setting, and this strategy in now being applied in the early and local advanced settings. A description of clinical and biological predictors of response is required in order to identify patients who may benefit the most from combination therapy.

A Circulating Risk Score, Based on Combined Expression of Exo-miR-130a-3p and Fibrinopeptide A, as Predictive Biomarker of Relapse in Resectable Non-Small Cell Lung Cancer Patients.

To date, the 5-year overall survival rate of 60% for early-stage non-small cell lung cancer (NSCLC) is still unsatisfactory. Therefore, reliable prognostic factors are needed. Growing evidence shows that cancer progression may depend on an interconnection between cancer cells and the surrounding tumor microenvironment; hence, circulating molecules may represent promising markers of cancer recurrence. In order to identify a prognostic score, we performed in-depth high-throughput analyses of plasma circulating markers, including exosomal microRNAs (Exo-miR) and peptides, in 67 radically resected NSCLCs. The miRnome profile selected the Exo-miR-130a-3p as the most overexpressed in relapsed patients. Peptidome analysis identified four progressively more degraded forms of fibrinopeptide A (FpA), which were depleted in progressing patients. Notably, stepwise Cox regression analysis selected Exo-miR-130a-3p and the greatest FpA (2-16) to build a score predictive of recurrence, where high-risk patients had 18 months of median disease-free survival. Moreover, in vitro transfections showed that higher levels of miR-130a-3p lead to a deregulation of pathways involved in metastasis and angiogenesis, including the coagulation process and metalloprotease increase which might be linked to FpA reduction. In conclusion, by integrating circulating markers, the identified risk score may help clinicians predict early-stage NSCLC patients who are more likely to relapse after primary surgery.

Serum levels of VCAM-1 are associated with survival in patients treated with nivolumab for NSCLC.

BACKGROUND: High circulating levels of cellular adhesion molecules (CAMs) in non-small cell lung cancer (NSCLC) have been supposed to act as a negative prognostic factor. Here, we explored the predictive role of pre-treatment levels of CAMs in previously treated patients receiving nivolumab for NSCLC. MATERIALS AND METHODS: Seventy one patients with advanced NSCLC, treated with nivolumab at the dose of 3 mg/kg every 14 days, were enrolled. Maximum follow-up time was 3 years. Serum levels of Vascular Cell Adhesion Molecule-1 (VCAM-1) and Intracellular Adhesion Molecule-1 (ICAM-1) were measured at baseline and before each nivolumab administration. Endpoints of the study were a composite outcome of survival ≥2 years or absence of disease progression at the end of the follow-up, and the overall survival. RESULTS: Composite outcome and overall survival were positively associated with VCAM-1 baseline levels and with the reduction of VCAM-1 during the treatment. After adjustment for potential confounders, the change in VCAM-1 serum levels during the treatment was an independent predictor of overall survival. CONCLUSIONS: High baseline serum levels of VCAM-1 are associated with a longer survival in patients treated with nivolumab as second line treatment for NSCLC. Surviving patients experience also a significant reduction in CAMs expression during the treatment. Hence, CAMs might be promising prognostic factors in patients with NSCLC underoing immunotherapy.

Novel Emerging Molecular Targets in Non-Small Cell Lung Cancer.

In the scenario of systemic treatment for advanced non-small cell lung cancer (NSCLC) patients, one of the most relevant breakthroughs is represented by targeted therapies. Throughout the last years, inhibitors of the epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), c-Ros oncogene 1 (ROS1), and V-raf murine sarcoma viral oncogene homolog B (BRAF) have been approved and are currently used in clinical practice. However, other promising molecular drivers are rapidly emerging as therapeutic targets. This review aims to cover the molecular alterations with a potential clinical impact in NSCLC, including amplifications or mutations of the mesenchymal-epithelial transition factor (MET), fusions of rearranged during transfection (RET), rearrangements of the neurotrophic tyrosine kinase (NTRK) genes, mutations of the Kirsten rat sarcoma viral oncogene (KRAS) and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA), as well as amplifications or mutations of human epidermal growth factor receptor 2 (HER2). Additionally, we summarized the current status of targeted agents under investigation for such alterations. This revision of the current literature on emerging molecular targets is needed as the evolving knowledge on novel actionable oncogenic drivers and targeted agents is expected to increase the proportion of patients who will benefit from tailored therapeutic approaches.

Safety and efficacy of immune checkpoint inhibitors in non-small-cell lung cancer: focus on challenging populations.

In recent years, immune-checkpoint inhibitors (ICIs) have represented one of the major breakthroughs in advanced non-small cell lung cancer treatment scenario. However, enrollment in registering clinical trials is usually restricted, since frail patients (i.e., elderly, individuals with poor performance status and/or active brain metastases), as well as patients with chronic infections or who take concurrent medications, such as steroids, are routinely excluded. Thus, safety and efficacy of ICIs for these subgroups have not been adequately assessed in clinical trials, although these populations often occur in clinical practice. We reviewed the available data regarding the use of ICIs in these 'special' populations, including a focus on the issues raised by the administration of immunotherapy in lung cancer patients infected with Sars-Cov-2.

Radiation-Related Deregulation of TUBB3 and BRCA1/2 and Risk of Secondary Lung Cancer in Women With Breast Cancer.

INTRODUCTION: Breast cancer survivors are at increased risk of developing unrelated primary cancers, particularly lung cancer. Evidence indicates that sex hormones as well as a deregulation of DNA-repair pathways may contribute to lung cancer onset. We investigated whether the hormone status and expression of markers involved in DNA repair (BRCA1/2, ERCC1, and P53R2), synthesis (TS and RRM1), and cell division (TUBB3) might be linked to lung cancer risk. PATIENTS AND METHODS: Thirty-seven breast cancer survivors with unrelated lung cancer and 84 control subjects comprising women with breast cancer (42/84) or lung cancer (42/84) were enrolled. Immunohistochemistry on tumor tissue was performed. Geometric mean ratio was used to assess the association of marker levels with patient groups. RESULTS: Estrogen receptor was expressed in approximately 90% of the breast cancer group but was negative in the majority of the lung cancer group, a result similar to the lung cancer control group. Likewise, ER isoform ß was weakly expressed in the lung cancer group. Protein analysis of breast cancer versus control had a significantly lower expression of BRCA1, P53R2, and TUBB3. Likewise, a BRCA1 reduction was observed in the lung cancer group concomitant with a BRCA2 increase. Furthermore, BRCA2 and TUBB3 increased in ipsilateral lung cancer in women who had previously received radiotherapy for breast cancer. CONCLUSION: The decrease of DNA-repair proteins in breast cancer could make these women more susceptible to therapy-related cancer. The increase of BRCA2 and TUBB3 in lung cancer from patients who previously received radiotherapy for breast cancer might reflect a tissue response to exposure to ionizing radiation.

Radiomic Detection of EGFR Mutations in NSCLC.

Radiomics is defined as the use of automated or semi-automated post-processing and analysis of multiple features derived from imaging exams. Extracted features might generate models able to predict the molecular profile of solid tumors. The aim of this study was to develop a predictive algorithm to define the mutational status of EGFR in treatment-naïve patients with advanced non-small cell lung cancer (NSCLC). CT scans from 109 treatment-naïve patients with NSCLC (21 EGFR-mutant and 88 EGFR-wild type) underwent radiomics analysis to develop a machine learning model able to recognize EGFR-mutant from EGFR-WT patients via CT scans. A "test-retest" approach was used to identify stable radiomics features. The accuracy of the model was tested on an external validation set from another institution and on a dataset from the Cancer Imaging Archive (TCIA). The machine learning model that considered both radiomic and clinical features (gender and smoking status) reached a diagnostic accuracy of 88.1% in our dataset with an AUC at the ROC curve of 0.85, whereas the accuracy values in the datasets from TCIA and the external institution were 76.6% and 83.3%, respectively. Furthermore, 17 distinct radiomics features detected at baseline CT scan were associated with subsequent development of T790M during treatment with an EGFR inhibitor. In conclusion, our machine learning model was able to identify EGFR-mutant patients in multiple validation sets with globally good accuracy, especially after data optimization. More comprehensive training sets might result in further improvement of radiomics-based algorithms. SIGNIFICANCE: These findings demonstrate that data normalization and "test-retest" methods might improve the performance of machine learning models on radiomics images and increase their reliability when used on external validation datasets.

Association Between Response to Nivolumab Treatment and Peripheral Blood Lymphocyte Subsets in Patients With Non-small Cell Lung Cancer.

Immune checkpoint blockade represents a major breakthrough in advanced non-small cell lung cancer (NSCLC) therapy. However, success is limited to a subset of patients and there is a critical need to identify robust biomarkers associated with clinical response. In this study, we assessed whether pre-existing immunological characteristics, as well as immune parameters measured during treatment, might provide such clinical guidance. We studied blood samples collected at baseline and during treatment in a cohort of advanced NSCLC patients (n = 74) treated with nivolumab. Several lymphocyte subsets and biomarkers were then correlated with overall survival (OS) as well as clinical response, assessed using RECIST criteria. We found that patients characterized by longer OS had higher levels of CD3+, CD4+, and CD8+ T cells but lower levels of NK cells at baseline. Moreover, that they displayed a statistically significant lower expression of PD-1 on both CD3+ and CD8+ T cells (p = 0.013 and p = 0.033, respectively). The pre-treatment level of exhausted T cells (CD8+PD1+Eomes+) was significantly lower in patients with controlled disease (CD), defined as partial response (PR), and stable disease (SD), compared to those with progressive disease (PD) (p = 0.046). In CD patients, the frequency of exhausted CD8+ T cells further decreased during treatment cycles (p = <0.0001, p = 0.0032, and p = 0.0239, respectively). In conclusion, our results suggest that the distribution of lymphocyte subsets and expression of PD-1 on T cells before treatment may help predict the outcome of anti-PD-1 treatment in NSCLC patients. In addition, assessing the initial levels of exhausted T cells as well as their decrease upon treatment may also predict response and clinical outcome.

ADP ribose polymerase inhibitors for treating non-small cell lung cancer: new additions to the pharmacotherapeutic armamentarium.

INTRODUCTION: Poly (ADP-ribose) polymerase inhibitors (PARPi) are already part of the armamentarium of drugs available against ovarian and breast cancer. There is less data available on the efficacy of these drugs in the treatment of non-small cell lung cancer (NSCLC). AREAS COVERED: The authors have analyzed the preclinical studies that justified the use of PARPi in NSCLC. They then evaluate the in vivo efficacy of the combination of these drugs with chemotherapy, radiotherapy, and immunotherapy. EXPERT OPINION: Data from clinical trials available to date have discouraged the use of PARPi in association with chemotherapy or radiotherapy in NSCLC. The knowledge available to date opens the door to the use of PARPi in association with immunotherapy. In fact, the activity of these drugs would not be based only on direct cytotoxic action, but also on the modification of the intra-tumor microenvironment, in particular by increasing the expression of PD-L1 on tumor cells. This action might potentially enhance available treatments with a modest increase in toxicity.

Correlation between B7-H4 and Survival of Non-Small-Cell Lung Cancer Patients Treated with Nivolumab.

Reliable predictors of benefit from immune checkpoint inhibitors in non-small-cell lung cancer (NSCLC) are still limited. We aimed to evaluate the association between the expression of selected molecules involved in immune response and clinical outcomes in NSCLC patients receiving nivolumab. In our study, the outcomes of 46 NSCLC patients treated with nivolumab in second or subsequent lines (Nivolumab Cohort) were compared with the expression of PD-L1, PD-L2, PD-1, B7-H3, and B7-H4 assessed by immunohistochemistry (IHC). Samples from 17 patients (37.0%) in the Nivolumab Cohort were positive for B7-H4 expression. At univariate analyses, only B7-H4 expression was associated with significantly decreased progression-free survival (PFS; 1.7 vs. 2.0 months; p = 0.026) and with a disadvantage in terms of overall survival (OS) close to statistical significance (4.4 vs. 9.8 months; p = 0.064). At multivariate analyses, B7-H4 expression was significantly associated with decreased PFS (hazard ratio (HR) = 2.28; p = 0.021) and OS (HR = 2.38; p = 0.022). Subsequently, B7-H4 expression was compared with clinical outcomes of 27 NSCLC patients receiving platinum-based chemotherapy (Chemotherapy Cohort), but no significant association was observed. Our results suggest a negative predictive role of B7-H4 in a population of NSCLC treated with immune checkpoint inhibitors, which deserves further research.

Baseline serum levels of osteopontin predict clinical response to treatment with nivolumab in patients with non-small cell lung cancer.

Treatment with nivolumab improves survival and response rate in non-small cell lung cancer (NSCLC). Nevertheless, due to its high financial cost, identifying predictors of response to treatment has become an urgent need. Here, we focused on serum osteopontin (OPN), a pleiotropic protein overexpressed in lung cancer and involved in the immune response. A cohort of NSCLC patients (n = 72) treated with nivolumab was enrolled. Blood samples were collected at the time of first five nivolumab administrations. OPN and high-sensitivity C-reactive protein (hs-CRP) were assayed at each time point. The primary endpoint was to assess the predictive value of baseline serum levels of OPN towards overall survival (OS). Secondary endpoints included the potential association between OPN, hs-CRP and response to nivolumab. OPN and hs-CRP correlate with each other, with neutrophil count and biochemical markers of metastatic disease. At baseline, serum OPN increased with increasing Eastern Cooperative Oncology Group scale of Performance Status (ECOG PS). When Eastern Cooperative Oncology Group scale of Performance Status) (RECIST) criteria were considered, high baseline OPN levels were associated with a worse response to nivolumab. Cox hazard regression further confirmed baseline serum OPN as a predictor of mortality with the best predictive accuracy for serum levels above 37.7 ng/mL. Patients above the cut-off value had a higher mortality rate as compared to low serum OPN levels during follow up. Serum OPN may have a predictive role in NSCLC patients treated with nivolumab. Although larger confirmatory studies are needed, measuring serum OPN levels at baseline can be a clinically useful tool in a near future.

Prognostic Relevance of Circulating Tumor Cells and Circulating Cell-Free DNA Association in Metastatic Non-Small Cell Lung Cancer Treated with Nivolumab.

: The treatment of advanced non-small cell lung cancer (NSCLC) has been revolutionized by immune checkpoint inhibitors (ICIs). The identification of prognostic and predictive factors in ICIs-treated patients is presently challenging. Circulating tumor cells (CTCs) and cell-free DNA (cfDNA) were evaluated in 89 previously treated NSCLC patients receiving nivolumab. Blood samples were collected before therapy and at the first and second radiological response assessments. CTCs were isolated by a filtration-based method. cfDNA was extracted from plasma and estimated by quantitative PCR. Patients with baseline CTC number and cfDNA below their median values (2 and 836.5 ng from 3 mL of blood and plasma, respectively) survived significantly longer than those with higher values (p = 0.05 and p = 0.04, respectively). The two biomarkers were then used separately and jointly as time-dependent covariates in a regression model confirming their prognostic role. Additionally, a four-fold risk of death for the subgroup presenting both circulating biomarkers above the median values was observed (p < 0.001). No significant differences were found between circulating biomarkers and best response. However, progressing patients with concomitant lower CTCs and cfDNA performed clinically well (p = 0.007), suggesting that jointed CTCs and cfDNA might help discriminate a low-risk population which might benefit from continuing ICIs beyond progression.

Serum PCSK9 levels at the second nivolumab cycle predict overall survival in elderly patients with NSCLC: a pilot study.

Monoclonal antibodies targeting PD-1 are used for treating NSCLC. To date, proprotein convertase subtilisin/kexin type 9 (PCSK9) has been poorly investigated in the oncologic field. Here, we aimed at evaluating whether serum PCSK9 might represent a predictive factor for OS in older patients with advanced NSCLC under nivolumab treatment. Among 78 patients with advanced, pre-treated NSCLC previously enrolled in a prospective study at Ospedale Policlinico San Martino in Genoa (Italy), 44 patients have been included in this sub-analysis due to the availability of serum samples for the measurement of PCSK9. Before each nivolumab administration, clinical information and blood samples were collected. Median age was 71, with a prevalence of the male sex. The most represented histological type of lung cancer was adenocarcinoma. The majority of patients were former smokers (72.1%). Median PCSK9 levels were 123.59 (86.32-169.89) ng/mL and 117.17 (80.46-147.79) ng/mL at cycle 1 and 2, respectively. Based on a receiver operating characteristic curve analysis, a PCSK9 value at cycle 2 of 95 ng/mL was found as the best cutoff point for OS. Kaplan-Meier analysis demonstrated that patients below the PCSK9 cutoff (< 95 ng/mL) experienced a better OS, as confirmed by Cox proportional hazard regression analysis. In this pilot study, circulating levels of PCSK9 < 95 ng/mL at the time of the second cycle of nivolumab treatment could independently predict a better OS in elderly patients with advanced, pre-treated NSCLC. However, further studies are warranted to validate these preliminary results.

Microtubule-targeting agents in the treatment of non-small cell lung cancer: insights on new combination strategies and investigational compounds.

INTRODUCTION: The management of non-small cell lung cancer (NSCLC) has been substantially improved in the last few years; it has been revolutionized by a patient-tailored approach, especially in the oncogene addicted disease, and by novel combinations containing immune checkpoint inhibitors. However, chemotherapy still represents a mainstay that persists over the decades with limited novelties. Tubulin inhibitors belong to different sub-classes of drugs that share the capability to interfere with mitosis by a direct action on the microtubule system. Among them, taxanes and vinca alkaloids still have a prominent role in clinical practice. AREAS COVERED: This review summarizes the mechanisms of action, current role and future directions of microtubule targeting agents; we focus on investigational agents in phase I and II clinical trials. EXPERT OPINION: Chemotherapy maintains a pivotal role in the treatment of NSCLC. New generation agents that have the potential to overcome the mechanisms of resistance to the available drugs may provide new therapeutic opportunities. Predictive biomarkers derived from combination strategies and phase III studies are necessary going forward.

Integrated Somatic and Germline Whole-Exome Sequencing Analysis in Women with Lung Cancer after a Previous Breast Cancer.

Women treated for breast cancer (BC) are at risk of developing secondary tumors, such as lung cancer (LC). Since rare germline variants have been linked to multiple cancer development, we hypothesized that BC survivors might be prone to develop LC as a result of harboring rare variants. Sixty patients with LC with previous BC (the study population; SP) and 53 women with either BC or LC and no secondary cancer (control population; CP) were enrolled. Whole exome sequencing was performed in both tumors and unaffected tissues from 28/60 SP patients, and in germline DNA from 32/53 CP. Candidate genes were validated in the remaining individuals from both populations. We found two main mutational signature profiles: S1 (C>T) in all BCs and 16/28 LCs, and S2 (C>A) which is strongly associated with smoking, in 12/28 LCs. The burden test over rare germline variants in S1-LC vs CP identified 248 genes. Validation confirmed GSN as significantly associated with LC in never-smokers. In conclusion, our data suggest two signatures involved in LC onset in women with previous BC. One of these signatures is linked to smoking. Conversely, regardless of smoking habit, in a subgroup of BC survivors genetic susceptibility may contribute to LC risk.

Afatinib and Erlotinib in the treatment of squamous-cell lung cancer.

INTRODUCTION: Squamous-cell carcinoma (SCC) of the lung represents around 20% of non-small cell lung cancers. Although activating mutations of EGFR are rare in this subtype, its overexpression occurs in more than half the cases. Consequently, many epidermal growth factor receptor (EGFR)-targeted agents have been investigated in patients with SCC. AREAS COVERED: This review summarizes the potential roles of erlotinib and afatinib in SCC of the lung. The authors explore the rationale of targeting EGFR in SCC and the pharmacological properties of erlotinib and afatinib. Subsequently, they describe the most relevant clinical data involving each agent with regard to their safety profile and antineoplastic activity. Particular focus is given to the LUX-Lung 8 trial, which compared erlotinib and afatinib as a second-line treatment in a population of patients affected by advanced SCC of the lung. EXPERT OPINION: Despite being overcome by new therapeutic strategies - in particular immune checkpoint inhibitors - afatinib and erlotinib still represent potential treatment options down the line in lung SCC because they have a more manageable toxicity profile compared to chemotherapy.

The evolving role of pemetrexed disodium for the treatment of non-small cell lung cancer.

INTRODUCTION: Non-small cell lung cancer (NSCLC) remains one of the big cancer killers, despite the introduction of a number of approved therapeutics in recent times. Pemetrexed is a multi-target folate inhibitor, which is currently available to patients affected by advanced non-squamous NSCLC in combination with a platinum derivate in first-line therapy and as a single agent in second-line therapy. Areas covered: This review covers presents the use pemetrexed in the management of NSCLC by exploring the data available from clinical trials and meta-analyses. Data from a phase III trial confirmed its role in the first-line setting in combination with immune checkpoint inhibitors (ICIs). Furthermore, data suggested a role for pemetrexed in local and advanced NSCLC. Expert opinion: To date, in spite of the introduction of novel anti-neoplastic agents, pemetrexed still represents a cornerstone in the management of non-squamous NSCLC. Furthermore, recently published data support its role in innovative combinations including together with chemotherapy and immunotherapy.

Downregulation of miR-99a/let-7c/miR-125b miRNA cluster predicts clinical outcome in patients with unresected malignant pleural mesothelioma.

Malignant pleural mesothelioma (MPM) is an aggressive tumor with a dismal overall survival (OS) and to date no molecular markers are available to guide patient management. This study aimed to identify a prognostic miRNA signature in MPM patients who did not undergo tumor resection. Whole miRNA profiling using a microarray platform was performed using biopsies on 27 unresected MPM patients with distinct clinical outcome: 15 patients had short survival (OS<12 months) and 12 patients had long survival (OS>36 months). Three prognostic miRNAs (mir-99a, let-7c, and miR-125b) encoded at the same cluster (21q21) were selected for further validation and tested on publicly available miRNA sequencing data from 72 MPM patients with survival data. A risk model was built based on these 3 miRNAs that was validated by quantitative PCR in an independent set of 30 MPM patients. High-risk patients had shorter median OS (7.6 months) as compared with low-risk patients (median not reached). In the multivariate Cox model, a high-risk score was independently associated with shorter OS (HR=3.14; 95% CI, 1.18-8.34; P=0.022). Our study identified that the downregulation of the miR-99a/let-7/miR-125b miRNA cluster predicts poor outcome in unresected MPM.