The MCF7/TAMR-7 Cell line is a breast cancer cell line resistant to tamoxifen. Tamoxifen is by far the most widely used drug for hormone-dependent breast cancer. However, primary or acquired resistance to Tamoxifen severely limits its clinical effectiveness. The MCF7/TAMR-7 cell line is a good model cell to study the signalling pathways, which are the major drivers of tamoxifen-resistant growth. The parental cell line for the MCF7/TAMR-7 cells is MCF7/S0.5, which was adapted to grow at low serum concentration in order to study the effect of estradiol and tamoxifen. MCF7/TAMR-7 has been established from a clone of cells that survived long term treatment with 1 μM tamoxifen. Tamoxifen-resistant cells are passaged continuously in presence of 1 μM tamoxifen, which is lethal for the parental MCF7/S0.5 cell line