Immune infiltration, interaction with the tumor cells, and selection pressure may be the responsible for the differences found in the expression of Klf4, Tacstd2, Zc3h12a, Il15, Il15ra, and Nfkbia. Since the implications of the regulation of the COX2-effector genes have been discussed elsewhere, we focus on the gene expression differences when we group individuals for CTCs existence. Here, KLF4 is linked to neoplasm.