ESR1 and breast cancer: In previous studies we and others observed that circulating oxysterols 27-hydroxycholesterol (HC) and 25-HC, exhibiting estrogen receptor (ER) modulating activities, were associated with breast cancer risk7 and prognosis8,9, while six oxysterols including 24S-HC, 7-ketocholesterol (KC), 5a,6a-epoxycholesterol (EC), 5b6b-EC, and lanosterol were associated with cardiovascular disease mortality in women with a breast cancer diagnosis10.