In the past few years, O-linked carbohydrate antigens, such as mucin antigen (MUC1), carcinoembryonic antigen (CEA), sialyl LewisX (SLX), CA19-9, Sialyl Tn (STn), and Tn have been reported to be associated with altered adhesion (Fogel et al, 1983; Rice and Bevilacqua, 1989), invasion (Bolscher et al, 1988; Matsushita et al, 1991; Nakamori et al, 1994), recurrence, and prognosis (Itzkowitz et al, 1990; Niklinski et al, 1992; Ogawa et al, 1994; Cao et al, 1995; Diez et al., 1996; Ohgami et al, 1999) in lung cancer and other tumours. This evidence concerns the gene CEACAM5 and lung cancer.