Annexin A1 (ANXA1, lipocortin 1) is a calcium-dependent, phospholipid-binding protein that inhibits phospholipase A2 and exerts anti-inflammatory activity. It is expressed in tissues such as the bone marrow and the immune system, lung, and the gastrointestinal tract and is localized to the cytoplasm, plasma membrane, and nucleus. Dysregulation of ANXA1 expression and changes in subcellular localization are associated with many cancers, some with increased expression and some with decreased expression depending on the tissue and state of disease progression. Staining is used to distinguish hairy cell leukemia from other B-cell malignancies. In normal tissues, ANXA1 stains positive in squamous epithelium of the esophagus, tonsil, placental trophoblasts, and infiltrating leukocytes across a variety of tissues. References: Int J Mol Sci. 2018;19(4):1045. doi: 10.3390/ijms19041045; Clin Sci (Lond). 2016;130(4):205-220. doi: 10.1042/CS20150415; J Exp Med. 2004;199(1):59-68. doi: 10.1084/jem.20031175; Lancet. 2004;363(9424):1869-1870 doi: 10.1016/S0140-6736(04)16356-3.