Calretinin belongs to the excitatory protein C superfamily. It is a calcium binding protein with a molecular weight of 29 kDa, which is abundant in neurons. Calretinin expressed tumors include mesothelioma, cardiac myxoma, ovarian sex cord stromal tumor, ameloblastoma, thymic papillary carcinoma and so on. The staining sites are cytoplasm and nucleus, with or without membrane positive. Nuclear staining is a necessary special expression of mesothelioma. It is suggested to be used in the differential diagnosis of epithelial malignant mesothelioma and malignant lung adenocarcinoma.