By global gene expression microarray analysis we found that in breast cancer cells (T47DCtrl) grown under ‘physiological’ (‘physio’) RA culture conditions, many RARA-target genes are in a repressed transcriptional state marked by epigenetic histone modifications, but are transcriptionally responsive to high ‘supraphysiological’ (‘supra’) exogenous RA (10-6M) in the culture medium (Figure 1A, based on Supplementary Table S1, and Supplementary Figure S1). The gene discussed is RARA; the disease is breast cancer.