Regression of Malignant Pleural Mesothelioma in Absence of Chemotherapy or Surgery: A Case Series

•What is already known about this subject?•Spontaneous regression of malignant pleural mesothelioma (MPM) is a rare outcome for patients with or without conventional treatment.•What are the new findings?•Here we report 2 cases of regression of biopsy confirmed MPM in the absence of chemotherapy or radiation.•What are the new findings and how might they impact on clinical practice in the foreseeable future?•More research is warranted on the heterogeneity of MPM and the role of the patient's own immune system to control the disease in certain circumstances.