WT1 and neoplasm: Moreover, all MPM cases showed positive immunostains for calretinin, cytokeratin 5/6 and Wilms tumor protein (WT1), thus confirming the mesothelial histogenesis of FE-related MPM; by contrast, no immunoexpression was recorded for cytokeratin 7 or thyroid transcription factor (TTF1), consequently excluding a possible pulmonary origin of neoplasms.