The proposed study population is as described. Exclusion of Lactating or Pregnant Women: Lactating and pregnant women are also excluded because of unknown effects of immunotherapy on a developing fetus or nursing infant. Children have been excluded from this study as mesothelioma is an adult cancer. Thus, the relevance of this drug to the pediatric population has not been established. Benefits: It is possible that this treatment will result in shrinkage of mesothelioma or in a stabilization of an otherwise progressing disease. It is not known, of course, whether these or any other favorable events will occur. It is not known whether this treatment will affect the overall survival of the patients. Costs: The patient will be responsible for the costs of standard medical care, including, CT scans, all drug administration fees and all hospitalizations, as well as for complications of treatment. Avelumab will be supplied to patients by Pfizer at no cost. Patients will not be responsible for the costs of blood procurement obtained for research purposes, the cost of special testing of any tissue for research purposes, or the cost for obtaining the tumor biopsy for research purposes. Incentives: No incentives will be offered to patients/subjects for participation in the study. Alternatives: Patients may be eligible for other investigational studies or focus on palliative care options. Confidentiality: Every effort will be made to maintain patient confidentiality. Research and hospital records are confidential. Patient’s name or any other personally identifying information will not be used in reports or publications resulting from this study. The Food and Drug Administration or other authorized agencies (e.g., qualified monitors) may review patients ‟ records and pathology slides, as required. 17.2 Privacy MSK‟s Privacy Office may allow the use and disclosure of protected health information pursuant to a completed and signed Research Authorization form. The use and disclosure of protected health information will be limited to the individuals described in the Research Memorial Sloan Kettering Cancer Center IRB Number: 17- 358 A(7) Approval date: 25 -Feb-2022 Page 47 of 51 Authorization form. A Research Authorization form must be completed by the Principal Investigator and approved by the IRB and Privacy Board (IRB/PB). The consent indicates that individualized, de-identified information collected for the purposes of this study may be shared with other qualified researchers. Only researchers who have received approval from MSK will be allowed to access this information, which will not include protected health information such as the participan t’s name, except for dates.