CYP24A1 and neoplasm: Recently, we found that colorectal tumours expressing high levels of CYP24A also expressed higher levels of proliferation markers.18 Therefore, to test whether there is a causal relationship between CYP24A1 overexpression and increased tumour growth, we compared xenografts overexpressing CYP24A1 with xenografts obtained from the same cells but with low basal CYP24A1 levels.