In order to identify molecular effectors of the paracrine signaling from CAFs that impinge on ER-α activity in luminal breast cancer cells, we screened the Institute for Molecular Medicine Finland (FIMM) Oncology compound library composed of 528 approved (28%) or emerging oncology drugs (55%) or probes (17%) at five concentrations covering a 10,000-fold concentration range. The gene discussed is ESR1; the disease is breast carcinoma.