MSLN and Pleural effusion: Other biomarkers have been proposed for indirect diagnosis of MPM by pleural effusion, including mesothelin [41, 42] (the only biomarker approved by FDA as a humanitarian use device [43]), osteopontin [44], megakaryocyte potentiating factor (an alternative cleavage product of the mesothelin precursor protein) [45] and fibulin-3 [46], among others [47].