PTGER4 and mesothelioma: To validate the diagnosis of mesothelioma versus that of adenocarcinoma, two positive mesothelioma markers (anticalretinin, anticytokeratin CK5/6, anti-Wilms tumour antigen-1, or antiepithelial membrane antigen) and two negative markers for adenocarcinoma (anti-Ber-EP4, monoclonal anticarcinoembryonic antigen, antithyroid transcription factor-1, or anti-MOC-31) are required [29].