The HMFG2 (Milk Fat Globule 2) monoclonal antibody, formerly known as clone 3.14.A3, specifically binds to Mucin-1 (MUC1) which is also known as CD227, Episialin, Breast carcinoma-associated antigen DF3, Cancer antigen 15-3, H23 antigen, Peanut reactive urinary protein (PUM), Polymorphic epithelial mucin (PEM), or Epithelial membrane antigen (EMA). MUC1 (CD227) is a heterodimeric cell surface glycoprotein that belongs to the epithelial mucin family. As a result of proteolytic cleavage, MUC1 (CD227) is comprised of a large, extracellular N-terminal alpha subunit that contains a domain of 20 amino-acid tandem repeats and functions in cellular adhesion. The smaller transmembrane C-terminal beta subunit contains a cytoplasmic domain that is involved in cell signaling. MUC1 (CD227) is variably expressed on the surfaces of normal and malignant glandular and ductal epithelial cells, myeloma cells, and some hematopoietic cell lineages including subsets of T cells, B cells, monocytes and dendritic cells. Soluble forms of MUC1 (CD227) may arise by shedding from the cell surface or by secretion of forms derived from alternative RNA splicing. MUC1 (CD227) plays roles in the provision of protective barrier function, the regulation of cellular adhesion and migration, and the transduction of multiple signal pathways. The HMFG2 antibody recognizes epitopes within the tandem repeat domain of MUC1 (CD227).