Malignant pleural mesothelioma (MPM) is a rare and incurable cancer. Most patients are diagnosed with unresectable disease for which treatment options are limited. The lack of prognostic biomarkers further complicates the decision-making. Recently, the introduction of immune checkpoint inhibitors (ICIs) has marked a shift but has failed to produce significant benefits for a large proportion of patients. Maximizing the efficiency of ICIs and developing new protocols to improve drug efficacy is the best possible strategy for improving the life expectancy and quality of life of patients with MPM. This study aims to characterize the organization of the immune system infiltrating mesothelioma and the dynamics of its interaction with the tumor. The rationale is that deciphering this complexity will help improve our understanding of the mechanisms underlying this disease and provide a new tool to optimize the use of ICIs in these patients.

Malignant Pleural Mesothelioma (MPM) is a rare and highly aggressive malignancy characterized by poor prognosis and limited therapeutic options. Most patients are diagnosed at an advanced, unresectable stage, with a median overall survival of approximately one year. Although the introduction of immune checkpoint inhibitors (ICIs) has represented a significant advancement, a substantial proportion of patients fail to derive meaningful clinical benefit. The lack of reliable prognostic and predictive biomarkers, together with marked molecular heterogeneity and limited understanding of disease biology, significantly hampers the development of effective therapeutic strategies. MPM is strongly associated with chronic inflammation driven by asbestos exposure, which profoundly alters the pleural microenvironment. Within this context, tumor cells and immune cells engage in dynamic and reciprocal interactions, generating a complex ecosystem that promotes disease progression and the emergence of aggressive phenotypes. The ability of tumor cells to modulate immune system activity is considered a key driver of MPM pathogenesis. This study aims to comprehensively characterize the organization of the tumor-infiltrating immune system and the dynamic interactions between tumor and immune cells. To achieve this goal, an integrative and multidimensional omics approach will be employed to generate a high-resolution map of MPM ecosystem and to identify novel biomarkers and potential therapeutic targets. This is an exploratory, non-interventional, non-pharmacological study with both prospective and retrospective components, conducted exclusively on biological samples collected during routine clinical practice. The study population will be structured into three complementary cohorts. A training prospective cohort (C1 - Training Set) including newly diagnosed MPM patients from whom fresh frozen (FF) tumor samples will be collected from diagnostic biopsies, surgical resections, or malignant pleural effusions, enabling in-depth characterization of the tumor and immune microenvironment. A validation independent retrospective cohort (C2 - Validation Set) including MPM samples collected between 2015 and 2022 and used to validate findings obtained in the training cohort. A nested cohort within C1 (C3 - HITHOC Set) that will include patients undergoing surgery combined with hyperthermic intrathoracic chemotherapy (HITHOC), allowing investigation of tumor-immune interactions and treatment response mechanisms in this specific clinical setting. By integrating data across these three cohorts, the study aims to identify immune-related markers associated with tumor aggressiveness, discover novel targets for next-generation immunotherapies, and characterize mechanisms underlying response to chemotherapy, with particular focus on the HITHOC setting. Expected outcomes include improved understanding of MPM biology, identification of novel biomarkers, and optimization of immunotherapy strategies, ultimately contributing to the development of more effective and personalized treatments for patients affected by this disease.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study
• Aged > 18 years
• Patients with histologically confirmed diagnosis of MPM
• Availability of biological material
• Clinical indicatio of eligibility for HITOCH protocol (only for C3 cohort)

Exclusion Criteria:

• Active current infection
• Autoimmune disease
• Women in childbearing age not able to exclude pregnancy

The study population includes patients diagnosed with Malignant Pleural Mesothelioma (MPM). Both prospective and retrospective cohorts will be included to ensure a comprehensive and biologically representative characterization of the disease. Eligible patients will have histologically confirmed MPM and available tumor biological samples obtained from diagnostic biopsies, surgical resections, or pleural effusions. Samples will include both fresh frozen (FF) material and formalin-fixed paraffin-embedded (FFPE) archival specimens.