ABCG2 and nodular goiter: In the present study, we choose 11 drug metabolism and transport genes, including ABCB1, ABCB4, ABCG2, CYP1A1, CYP1B1, CYP24A1, CYP27B1, CYP39A1, SLC1A2, SLC19A3, and SLC26A2, to detect their methylation status of promoter region in a cohort of nodular goiter and normal thyroid tissues using methylation-specific PCR (MSP).