WT-1 Immunohistochemistry is used for helping in identification and differentiation of a variety of tumors by pathologists as follows with three staining patterns. Nuclear stain against N-terminus by mouse monoclonal clone 6F-H2 is used for differentiating 1) malignant mesothelioma (WT-1 pos) from non-small cell lung carcinoma (WT-1 neg); 2) Ovarian serous carcinoma (WT-1 pos) from endometrioid, mucinous, and clear cell carcinoma of the ovary (WT-1 neg); 3) Wilms tumor (WT-1 pos) from mesoblastic nephroma (WT-1 neg); 4) Ovarian transitional cell carcinoma (WT-1 pos) from malignant Brenner tumor (WT-1 neg); 5) Pleural endometriosis (WT-1 pos) from biphasic pulmonary blastoma and lung adenocarcinoma (WT-1 neg). Cytoplasmic stain against N-terminus by mouse monoclonal clone 6F-H2 is used to differentiate 1) Benign and malignant vascular tumor (WT-1 pos) from vascular malformations (WT-1 neg); 2) Mammary myofibroblastoma (WT-1 pos) from breast lobular carcinoma (WT-1 neg). Nuclear stain against C-terminus by rabbit polyclonal antibody C-19 is used to differentiate desmoplastic round cell tumor (WT-1 pos) from Ewing sarcoma (WT-1 neg).