Although an IGF-1-activated gene signature identified in MCF-7 cells following stimulation with IGF-1 has been correlated with poor prognosis in breast cancer [59], other reports have shown that a gene signature associated with high IGF1 expression in breast cancer samples is associated with more favorable outcomes, with the authors suggesting that higher levels of IGF1 drive a more differentiated, less aggressive phenotype in ER+ tumors [60]. This evidence concerns the gene ESR1 and breast cancer.