Calretinin is a calcium-binding protein serving diverse cellular functions including message targeting and intracellular calcium buffering, and is involved in processes such as cell arrest and apoptosis. Calretinin functions as a modulator of neuronal excitability and may play a protective role in the survival of nerve cells during disturbances in calcium homeostasis. It is abundantly expressed in subsets of neurons throughout the brain and spinal cord, particularly retina and sensory ganglia, but it is also found in mesothelium, eccrine sweat glands, Sertoli cells, ovarian stromal cells and adrenal cortical cells. Due to its high sensitivity against mesothelial cells, calretinin is a useful marker in differentiating mesothelioma (especially of the epithelial type) and metastatic adenocarcinoma to the serous membranes. It is also a diagnostic marker of Hirschsprung disease and some ovarian and testicular cancers such as Sertoli-Leydig cell tumor, Sertoli cell tumor, Leydig cell tumor, sex cord tumor with annular tubules, as well as steroid cell tumor. In tumors, calretinin has been detected in mesotheliomas and some pulmonary adenocarcinomas.