MUC1 is a glycoprotein found at the secretory poles of normal cells but is hypoglycosylated on the entire surface of cell membranes of adenocarcinomas. In order to determine the influence on the immune response of peptide context for epitope presentation, peripheral blood mononuclear cells (PBMC) from patients with adenocarcinomas, were stimulated with MUC1 peptides derived from the 20 amino acids (aa) long sequence that is characteristic of the MUC1 Variable Number of Tandem Repeats (VNTR). In the seven peptides tested, the T-cell tumor-specific epitope (cTSE) was surrounded by variable numbers of aa and repeated up to 5 times in the same peptide. The results of this study indicate that cultures stimulated with peptide 610 (GSTAPPAHGVTS APDTRPAP) showed the highest specific killing of the MUC1-expressing breast cancer MCF-7 cells. Peptide 610 is also superior to the other peptides in inducing better production of the type 1 cytokines, tissue necrosis factor alpha and interferon gamma. In conclusion, context of the epitope and not sequence alone determines immunogenicity.