CYP27B1 and neoplasm: Various vitamin D3 target tissues express CYP27B1 and can therefore metabolize 25‐D3 to 1,25‐D3, which then acts in an autocrine/paracrine‐manner.1 Increasing dietary vitamin D3 elevates the plasma 25‐D3 levels and thereby increases the amount of substrate for CYP27B1 at local sites including tumour xenografts.