ER gene expression in MCF-10A cells maintained in and exposed to various culture/treatment conditions was assessed using a human estrogen signaling pathway-specific gene expression profiling system (SuperArray, Inc; Bethesda, MD) as described in the Methods section. Results shown are those of three different experiments comparing two different culture conditions at a time and using 5-10 μg total RNA. MCF-10A cells grown in culture media either containing or lacking HC/EGF were either left non-treated (NT) or treated twice a week with 1 nM E2 for 2 weeks. Numbers in parentheses indicate the number of passages in that particular medium type. Mean signal intensity (pixels × 10-4) values from duplicate spots of both ERα and ERβ per membrane were normalized against those of a housekeeping gene and taken to be representative of mean gene expression.