To provide further information on the possible differences between DES- and E2-induced ERα-mediated effects, the present study also assesses the relative potency of the two compounds as ERα agonists in a human osteosarcoma U2OS ERα reporter gene assay and in a proliferation assay of human ERα positive T47D breast cancer cells and quantifies DES- and E2-induced modulation of gene expression in T47D cells using next generation sequencing (RNA-seq) and transcriptome analysis. The gene discussed is ESR1; the disease is breast carcinoma.