In recent years, we have reported that this initiation step can be regulated through trafficking of the GalNAc-Ts between the ER and the Golgi (Gill et al., 2010) and that marked ER localisation explains the high Tn phenotype in at least 60% of human breast tumours (Gill et al., 2013). The gene discussed is B4GALNT1; the disease is breast neoplasm.