CYP27B1 and cancer: Recent studies indicate quantitative associations between exposure to vitamin D3 and the incidence of HNC: cancer risk assessment included circulating calcidiol plasma/serum concentrations, vitamin D3 intake, the presence of the VDR gene polymorphism, and genes involved in the vitamin D3 metabolism pathway, CYP27B1 and CYP24B1 [194,286,287,288].