Objective     To establish a Tamoxifen (TAM)-resistant cell line of MCF-7 human breast cancer and to investigate the drug resistance of the cell line.     Methods     MCF-7 Tamoxifen-resistant (MCF-7/TAM-R) cell line was induced by a high concentration of 4-hydroxytamoxifen (OHT) treatment for a short period. Drug resistance of MCF-7/TAM-R cells were determined by cell morphology

cell growth curve

cell doubling time

drug toxicity tests

cell cycle and expression of apoptosis-related proteins BIK and Caspase-7.     Results    MCF-7/TAM-R cell line was successfully established

and its drug resistance index (RI) was 13.88±2.93 (P0.05). Compared with its parental cell line

MCF-7/TAM-R cell line exhibited a different cell morphology

a higher proliferation ability (P0.05)

a shorter cell doubling time (P0.05) and a stronger resistance to OHT-mediated cytotoxic effects (P0.05). OHT failed to induce the expression of BIK and Caspase-7 (P0.05) in MCF-7/TAM-R cell line.     Conclusion     MCF-7/TAM-R cell line induced by a high concentration of OHT for a short period has a significant resistance to TAM.