Specificity: VNTR5 and VNTR20 recombinant unglycosylated fragments of MUC1 protein and underglycosylated MUC1 prepared from tumor fluids or as a result of chemical treatment of human milk MUC1. These MAbs do not recognize natural MUC1 protein isolated from human milk by affinity purification on carbohydrate epitope specific MAbs and belong to MAb cluster 1-4 according to ISOMB TD-4 classification. No cross-reactivity with egg white avidin. MAbs M4H2, M2F1, M2C5, M2E104 and M3A106: Affinity >1 X 108 all MAbs. MAbs bind with high efficiency with different epitopes within the VNTR tandem repeat peptide region of MUC1 molecule, which have different conmations and peptide- carbohydrate compositions. MAb M4H2 reacts with VNTR20 recombinant unglycosylated fragment of MUC1 protein (and very weakly with monomeric MUC1 peptide), with deglycosylated and underglycosylated natural MUC1 (but not with completely glycosylated natural milk MUC1). MAbs M2F1, M2C5, M2E104, M3A106 efficiently recognize underglycosylated and natural MUC1 protein isolated from human milk by affinity chromatography. All these MAbs belong to MAb clusters 6 and 7 according to ISOMB TD-4 classification. Non cross-reactive with normal serum proteins and human tissues of non-epithelial origin.