KRT19 and neoplasm: The lack of a complete overlap between the presence of CK-19 mRNA-positive CTCs and DTCs either before (Ismail et al, 2004; Pierga et al, 2004; Muller et al, 2005; Wiedswang et al, 2006) or after chemotherapy (Slade et al, 2009) could be related to the fact that occult tumour cells are rare events and therefore their evaluation is greatly influenced by sampling variability.