Trial Assessing Fianlimab Plus Cemiplimab Plus Chemotherapy or Cemiplimab Plus Chemotherapy in Patients With Pleural Mesothelioma

Inclusion Criteria: 1. Signed written Informed Consent. * Subjects must have signed and dated an IEC approved written informed consent form in accordance with regulatory and institutional guidelines. This must be obtained before the performance of any protocol-related procedures that are not part of normal subject care. * Subjects must be willing and able to comply with scheduled visits, treatment schedule, and laboratory testing. 2. Histological diagnosis (no cytology allowed, thoracoscopy biopsy recommended). 3. Non resectable PM as evaluated by a specialist MTB comprising a specialized thoracic surgeon. 4. Measurable disease by CT with iodure injection according to RECIST 1.1 modified criteria for mesothelioma (pleural thickness perpendicular to the chest wall or mediastinum of 7 mm or more, on 2 positions, at 3 separate levels on transverse cuts of CT-scan, at least 1 cm apart, the sum of 6 measurements defining a pleural unidimensional measure), or according to RECIST1.1 criteria for mediastinal nodes or metastatic lesion. 5. ECOG PS 0 and 1. 6. Weight loss \<10% within 3 months of study entry. 7. Chemo-naive and immuno-naive. 8. Age ≥18 years, \<76 years. 9. Life expectancy \>3 months. 10. Available pathological samples (at least 10 slides from the thoracoscopy pleural biopsy sample). 11. Adequate biological functions: creatinine clearance ≥45 mL/min (Cockroft or MDRD or CKD-epi); neutrophils ≥1500/mm3; platelets ≥100 000/mm3; haemoglobin ≥9g/dL; AST and ALT \<3 x ULN, total bilirubin \<2 x ULN (patients with hepatic metastases or Gilbert's syndrome must have AST and ALT ≤5 x ULN and a baseline total bilirubin ≤2 x ULN). 12. WOCBP\* must have a negative serum (beta-hCG) at screening. \*WOCBP are defined as women who are fertile following menarche until becoming postmenopausal, unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy, and bilateral oophorectomy. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high FSH level in the postmenopausal range may be used to confirm a postmenopausal state in women not using hormonal contraception or hormonal replacement therapy. However, in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient to determine the occurrence of a postmenopausal state. The above definitions are according to the CTFG guidance. Pregnancy testing and contraception are not required for women with documented hysterectomy or tubal ligation. 13. Male study participants with WOCBP partners are required to use condoms during the study and until 6 months after the last dose of study treatment unless they are vasectomised or practice sexual abstinence. 14. Vasectomised partner or vasectomised study participant must have received medical assessment of the surgical success. NB: Periodic abstinence (calendar, symptothermal, post-ovulation methods), withdrawal (coitus interruptus), spermicides only, and LAM are not acceptable methods of contraception. Female condom and male condom should not be used together. 15. WOCBP must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the entire trial and until 6 months after last treatment. 16. All men must agree not to donate sperm during the trial and for 6 months after receiving the last therapy dose. 17. As recommended in current French guidelines, a firm recommendation of radiation therapy for thoracocentesis tracts (3 x 7Gy) is made for patients with thoracocentesis or thoracoscopy within 2 months before accrual, with a firmly recommended interval between thoracoscopic procedure (removal of drains) and radiation of no more than 42 days. A 7-day interval between the end of radiotherapy and the initiation of treatment should be respected. Exclusion Criteria: 1. ECOG PS\>2. 2. Previous cancer treatment including chemotherapy or immunotherapy with anti-PD-1, anti-PD-L1, Anti-CTLA4 or any ICI antibody. 3. Pleural effusion as the only radiological abnormality without measurable pleural thickness or mediastinal node enlargement. 4. Peritoneal, pericardial or tunica vaginalis testis mesothelioma. 5. Previous diagnosis of adenocarcinoma from any anatomic site within the previous 5 years, with the exception of prostate adenocarcinoma history within the previous 5 years, in case of localized prostate cancer, with good prognostic factors according to d'Amico classification (\<T2a, score de Gleason ≤6 and PSA ≤10 ng/ml) provided they were treated in a curative way (surgery or radiotherapy, without any chemotherapy). Previous or active cancer within the previous 5 years (except for treated carcinoma in situ of the cervix, or basal cell skin cancer treated or not). 6. Uncontrolled pleural effusion requiring frequent thoracocentesis (needing thoracoscopic pleural pleurodesis before possible accrual). 7. Symptomatic untreated brain metastasis (without previous whole brain radiotherapy or stereotactic ablative brain radiotherapy or without surgical resection). At least 2 weeks delay between the end of radiotherapy and the beginning of immuno-chemotherapy treatment should be respected. Asymptomatic brain metastasis, not needing corticosteroids greater than 10 mg prednisone equivalent daily or mannitol infusions, are allowed. 8. Radiotherapy needed at initiation of tumour treatment, except bone palliative radiotherapy on a painful or compressive metastasis, or radiotherapy on thoracic drain or puncture routes. 9. History of previous primary immunodeficiency, organ transplantation needing an immunosuppressive treatment, any immunosuppressive drug within 28 days before randomisation date, or history of severe toxicity (grade 3/4) by immune mechanism linked to another immunotherapy treatment for any kind of disease. 10. Systemic treatment with corticosteroids with greater dose than 10 mg prednisone equivalent daily, within 14 days before initiation of the treatment. Inha