In addition, although both receptors facilitate chemoresistance to the selective estrogen receptor modulator (SERM) tamoxifen in breast cancer, resistance to tamoxifen is characterized by decreased expression of IGF-1R and increased EGFR expression, and more surprisingly, no detectable difference was found in EGFR expression between breast cancer cells resistant and sensitive to tamoxifen when measured with cytometry (79). This evidence concerns the gene ESR1 and breast carcinoma.