Immunohistochemical testing for HBME-1 (Human Bone Marrow Endothelial Cell-1) aims to detect this antigen on the surface of mesothelial cells (cells lining serous cavities such as the pleura and peritoneum) and in the epithelial cells of certain tumors. It is primarily used as an aid in the diagnosis of papillary thyroid carcinoma (PTC) and to differentiate it from benign lesions, as well as in the diagnosis of mesothelioma.