A previous study examined the expression profile of 21 CYP genes in breast cancer cells using a tissue microarray containing 170 breast cancers and reported that the highest percentage of strong immunopositivity was seen for CYP4X1, CYP2S1 and CYP2U1, while CYP2J and CYP3A43 frequently displayed no immunoreactivity17. Here, CYP2U1 is linked to breast cancer.