Anterior gradient protein 3 homolog is a protein that in humans is encoded by the AGR3 gene. The deduced 166-amino acid protein has an N-terminal signal sequence. Fluorescence-tagged BCMP11 localized in secretory or endosome-like organelles in transfected breast carcinoma cell lines. Immunohistochemical analysis showed that expression of BCMP11 was restricted in normal tissues, with significant staining of only the epithelial lining of colonic mucosa. However, BCMP11 was detected in 43 of 58 (74%) breast cancer tissues tested, but not in normal breast ductal epithelial cells. In cancerous epithelial cells, BCMP11 localized to the cytoplasm.