The most common test used to diagnose Paget's disease is the biopsy, removal of a tissue sample from the affected area which is then examined under the microscope by a pathologist, who distinguishes Paget cells from other cell types by staining tissues to identify specific cells (immunohistochemistry). CD138 and p53 can be used, both being positive in Paget's disease, and negative in Toker cells, which are normal epithelial cells with clear cytoplasm that can be difficult to distinguish from Paget's disease. Besides, Paget cells stain positive for CK7 in >90% of the cases. Similarly, GATA3 and HER-2 are expressed in around 90% of the cases, and can be used for the confirmation, including CK7 negative Paget disease.