Using cytosolic fractions derived from human tissues of the breast, liver, or placenta; cultured human cancer cells; or hamster kidney tissues as enzyme sources, several studies have shown that flavonols (e.g., quercetin), isoflavones (e.g., genistein), catechins (e.g., (-)-epigallocatechin-3-gallate), and phenolic acids (e.g., chlorogenic acid) are also COMT inhibitors with a mixed-type inhibition mode with IC50 values at micromolar concentration ranges [16,18,24,25]. The gene discussed is COMT; the disease is cancer.