The aromatase PI.1 promoter utilization is very unique features in SK-BR-3 cells and therefore, SK-BR-3 cells would be valuable to study a paracrine mechanism of estrogens biosynthesis and effects of bioactive factors on cell-specific promoter activity, although main promoter utilization of aromatase gene expression is PI.3, PI.4 and PII in the human breast cancer tissues and cell lines including MCF-7, T-47D and MDA-MB-231 cells [21]. The gene discussed is CYP19A1; the disease is breast cancer.