Under physiological conditions, COMT can metabolize EGCG to 4′′-o-methyl-EGCG (MeEGCG) and 4′,4′′-di-o-methyl-EGCG (DiMeEGCG), resulting in a reduction of the oral bioavailability of EGCG and reduced cancer-related biological activities of EGCG. The gene discussed is COMT; the disease is cancer.