PRF1 and malignant mesothelioma: The commonality between PL and MM patients means that the increases in CD45RA− and perforin+ cells may be related to asbestos exposure, whereas the difference in post-stimulation maintenance of perforin between these patients underlines the immunological states of PL and MM, related to the pathologies of asbestos exposed patients not or suffering from malignant mesothelioma, respectively.