LDL-induced growth in both ER-α-positive and ER-α-negative cells was inhibited when CYP27A1, the enzyme responsible for the rate-limiting step in 27OHC biosynthesis, was silenced using siRNA, suggesting that 27OHC could contribute to the risk of breast cancer by mediating LDL-induced breast cancer proliferation. The gene discussed is ESR1; the disease is breast cancer.