27-Hydroxycholesterol (27-HC) is an endogenous oxysterol with multiple biological functions, including activity as a selective estrogen receptor modulator (SERM) (a mixed, tissue-specific agonist-antagonist of the estrogen receptor (ER)) and as an agonist of the liver X receptor (LXR).

[1] It is a metabolite of cholesterol that is produced by the enzyme CYP27A1.

[1] A link between high cholesterol and breast cancer has been identified, and it has been proposed that this is due to 27-HC production by CYP27A1.

[2] Because of its estrogenic action, 27-HC stimulates the growth of ER-positive breast cancer cells, and has been implicated in limiting the effectiveness of aromatase inhibitors in the treatment of breast cancer.

[1] As such, identified CYP27A1 inhibitors, including the marketed drugs anastrozole, fadrozole, bicalutamide, dexmedetomidine, ravuconazole, and posaconazole, have been proposed as potential adjuvant therapies in ER-positive breast cancer.