IL-20 was significantly over-expressed in ER-positive cancer cells and tissues, possibly through estrogen signaling mediated by the ERα estrogen receptor, encoded by ESR1. To test this hypothesis, we examined the effect of ESR1-specific siRNA, or of the ERα antagonist ICI 182,780 (ICI), on the expression of IL-20 mRNA MCF-7 cells. The gene discussed is ESR1; the disease is cancer.