MAb VU-4H5 reacts with MUC1, a large transmembrane glycoprotein expressed on the ductal surface of normal glandular epithelia. The dominant epitope of MAb VU4H5 is APDTR as established with ‘epitope fingerprinting’. VU-4H5 preferentially binds to under-glycosylated ‘tumor’ MUC1. The extracellular domain of MUC1 largely consists of a highly conserved, O-glycosylated 20 amino acids tandem repeat which can occur 30-100 times per molecule depending on the length of the allele involved. In the vast majority of human carcinomas this protein is upregulated and poorly glycosylated and appears on the cell surface in a non-polarized fashion. Antibody to EMA is useful as a pan-epithelial marker for detecting early metastatic loci of carcinoma in bone marrow or liver.