The assay used in the present study, that is, RT–PCR detection of CK19 mRNA, has been developed in our laboratory for the detection of occult carcinomatous cells in mediastinal lymph nodes in non-small-cell lung carcinoma (Saintigny et al, 2005) and by other teams in various carcinomas (Van Trappen et al, 2001; Inokuchi et al, 2003; Favia et al, 2004). The gene discussed is KRT19; the disease is non-small cell lung carcinoma.