DKK3 and central nervous system cancer: The secretory protein REIC/Dkk-3 mechanism of action for inhibiting Wnt signaling pathway is currently unknown, but its expression has been shown to be downregulated in various cancer cell lines, including prostate, renal, liver, pancreas, cervical, lung, melanoma, glioma, testicular, colon, and even osteosarcoma cancer cells [10–20].