IGFBP1 and breast cancer: To determine if IGFBP-1 is critical for the development of tamoxifen resistance in breast cancer cells, the level of IGFBP-1 in MCF-7 parental cells (MCF7-P) and MCF-7 tamoxifen resistant cell (MCF7-TamR), as well as in T-47D parental (T47D-P) and T47D-TamR was determined.