It is well known that epithelial tumor cells migrating through the bloodstream undergo EMT which is characterized, among others, by a loss of expression of epithelial markers32, 54, 55; therefore, it is reasonable to hypothesize that, in this small subgroup of patients without detectable CTCs by CS, the TTF-1+/EpCAM− CTCs probably represent CTCs undergoing EMT. Here, TTF1 is linked to neoplasm.