CYP27A1 and cancer: The observation that 27HC inhibits the growth of ER-negative breast cancers likely due to its ability to disrupt cholesterol homeostasis, while somewhat expected, was difficult to understand in light of the established links between elevated cholesterol (and 27HC) and cancer progression, and the observation that elevated expression of CYP27A1 is associated with the most aggressive, high grade, ER-negative tumors.