Calcitriol increases the expression of stemness-related genes, such as the leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), SMOC2, LRIG1, MEX3A, MSI1, and PTK7, attenuating the transformation into cancer stem cells, and, therefore, impacts tumorigenesis at a very early stage [143]. The gene discussed is MEX3A; the disease is cancer.