To investigate whether the cell cycle inhibition of ER-positive breast cancer cells by TAM is affected by the level of RFC3 expression, we showed by flow cytometric cell cycle assay that, compared with the control group, the proportion of MCF-7 cells in S-phase decreased and the proportion of MCF-7 cells in G1-phase increased after RFC3 overexpression in MCF-7 cells treated with TAM. This evidence concerns the gene RFC3 and breast cancer.