TTF1 and malignant mesothelioma: International Mesothelioma Interest Group Guideline for pathologic diagnosis of malignant mesothelioma has recommended various immunohistochemical negative markers, CEA, MOC-31, TTF-1, Napsin-A to differentiate it from adenocarcinoma and p40, p63, MOC-31 to differentiate it from squamous cell carcinoma4.