Recently, RT–PCR assays with tumour-specific gene markers such as CK19, CEA, MUC1, PIP, Mapsin and mammaglobin B have been widely used to detect occult metastasis in cancer patients (Noguchi et al, 1994,1996; Schoenheld et al, 1994; Mori et al, 1995,1998; Kataoka et al, 2000; Masuda et al, 2000; Manzotti et al, 2001; Mitas et al, 2001). Here, MUC1 is linked to cancer.