['To investigate the inhibitory effect of green tea extract, epigallocatechin gallate (EGCG), on wild-type human leiomyoma (WT-HuLM) cells and its potential action via catechol-o-methyltransferase (COMT) activity.', 'Cell proliferation of WT-HuLM and COMT gene-silenced HuLM (COMT-shRNA-HuLM) cells treated with 0 or 100 µM EGCG for 7 days was measured using the MTT method. Total RNA and protein were extracted from cells treated with 0 or 100 µM of EGCG for 48 h. Gene expression profiling was performed using Human Signal Transduction PathwayFinder. Proliferation cell nuclear antigen (PCNA), cyclin-dependent kinase 4 (Cdk4) and COMT protein levels were detected by Western blot analyses. COMT enzyme activity was evaluated by HPLC.', 'EGCG-treated WT-HuLM cells showed significantly decreased COMT expression (p < 0.001) and enzyme activity (p < 0.05) compared to untreated WT-HuLM cells, while COMT-shRNA-HuLM cells showed no significant change. At 100 μM of EGCG, survival of WT-HuLM cells was significantly lower (p < 0.05) compared to COMT-shRNA-HuLM cells. EGCG treatment modulated multiple signaling pathways in WT-HuLM compared to untreated control, while changes were minimal or reversed in COMT-shRNA-HuLM cells. EGCG significantly decreased PCNA, Cdk4 and soluble COMT protein levels (p < 0.001) in WT-HuLM, but not in COMT-shRNA-HuLM cells.'] Is green tea extract inhibition of human leiomyoma cell proliferation mediated via catechol-O-methyltransferase?