Thus, the purpose of our study was: (i) to compare the protein profiles of two breast cancer cell lines with different ER expression when exposed to equivalent concentrations of isoflavones; (ii) to identify which proteomic modulations are specific to breast cancer cell inhibition or proliferation, by comparing the proteomic profile of MCF-7 cells exposed to IC20 and SC20 of test compounds. The gene discussed is ESR1; the disease is breast cancer.