The article reports the full-length sequence of the tumor-associated polymorphic epithelial mucin (PEM), a glycoprotein expressed by human mammary cells and aberrantly in tumors. PEM contains a large domain of variable numbers of 20-amino acid repeat units, which are highly glycosylated due to the presence of serine and threonine residues. The core protein of PEM consists of three distinct regions: an amino-terminal region with a putative signal peptide and tandem repeats, a major portion of the protein with the tandem repeat region, and a carboxyl-terminal region with degenerate tandem repeats, a transmembrane sequence, and a cytoplasmic tail. The sequence analysis reveals that the tandem repeat region is highly repetitive and immunogenic, with potential O-glycosylation sites making up more than one-fourth of the amino acids. The length variations in the tandem repeat result in PEM being a variable number tandem repeat (VNTR) locus, which is valuable for genetic studies. The article also discusses the potential glycosylation sites and the immunogenicity of PEM, highlighting its significance as a target antigen for both antibodies and T lymphocytes in cancer diagnosis and therapy.The article reports the full-length sequence of the tumor-associated polymorphic epithelial mucin (PEM), a glycoprotein expressed by human mammary cells and aberrantly in tumors. PEM contains a large domain of variable numbers of 20-amino acid repeat units, which are highly glycosylated due to the presence of serine and threonine residues. The core protein of PEM consists of three distinct regions: an amino-terminal region with a putative signal peptide and tandem repeats, a major portion of the protein with the tandem repeat region, and a carboxyl-terminal region with degenerate tandem repeats, a transmembrane sequence, and a cytoplasmic tail. The sequence analysis reveals that the tandem repeat region is highly repetitive and immunogenic, with potential O-glycosylation sites making up more than one-fourth of the amino acids. The length variations in the tandem repeat result in PEM being a variable number tandem repeat (VNTR) locus, which is valuable for genetic studies. The article also discusses the potential glycosylation sites and the immunogenicity of PEM, highlighting its significance as a target antigen for both antibodies and T lymphocytes in cancer diagnosis and therapy.