It has been proved that MUC1 is extremely useful for glycosylation studies because changes in the expression and activity of specific glycosyltransferases have been related to changes in the O-glycan structures expressed by MUC1. In a previous report we found that Lewis x antigen was highly expressed by normal epithelial tissues of mammary gland and digestive tract. In order to continue the study of blood group related Lewis antigen involvement in breast cancer, we have focused this research on the difucosylated Lewis y antigen; this carbohydrate specifically belongs to the ABH Lewis blood group family which is overexpressed on the majority of carcinomas including ovary, pancreas, prostate, breast, colon and non small cell lung cancers.