Calretinin (CALB2, calbindin) is a calcium-binding protein belonging to the troponin C superfamily that is involved in calcium signaling. The protein is found in normal neurons, macrophages, ganglion cells, mesothelial cells, the retina, hair follicles, adipose tissue, breast, adrenal cortex and testis. Staining can be cytoplasmic, membranous and nuclear. It is a useful marker for differentiating mesotheliomas (positive) from lung adenocarcinomas (negative). It is also positive in adrenal cortical lesions, ovarian Sertoli-Leydig tumors, sex cord-stromal tumors, Schwannomas, and reactive mesothelial cells. References: Am J Sug Path 2003, 27:1031; Am J Clin Path 2001, 116:709, Am J Surg Path 2010, 34:423, Arch Path Lab Med 2007, 131:979; Am J Clin Path 2004, 122:552.