DKK1 and neoplasm: Recent studies have examined the cell-free mRNA expression of several genes, including TS [28], β-catenin [29], hTERT [26,30,31], CK19 [32,33], MUC1 [34], CXCR4 [35], Bmi-1 [35], Her-2 [36] and DKK1 [24], these studies have focused on the use of cell-free mRNA for early diagnosis, tumor staging and disease monitoring.