Expression of STn has been shown to be dependant on the expression of the sialyltransferase ST6GalNAc I in breast cancer cell lines (Julien et al, 2001, 2005; Sewell et al, 2006) and totally correlated with ST6GalNAc I expression in primary breast tumours (Sewell et al, 2006). Here, ST6GALNAC1 is linked to breast carcinoma.