Stimulation of the ER+ breast cancer cell line MCF-7 with FGF10 enhanced the interaction of the transcription factors NFIB and YBX1 with the ER, which inhibited its transcriptional activity and shunted the cells toward a more ER−, basal-like cancer phenotype with reduced estrogen dependency and lower sensitivity to anti-estrogen therapy. This evidence concerns the gene ESR1 and breast cancer.