26-hydroxycholesterol (26-HC) is synthesized by a mitochondrial P-450 enzyme, cytochrome P-450 27A1 (CYP27A1), a gene encoding a cytochrome P-450 oxidase, [103] and is associated with breast cancer etiology [78], acting in immune cells favoring breast cancer metastasis. The gene discussed is CYP27A1; the disease is breast cancer.