To explore the regulatory mechanism of CYP1B1-AS1 down-regulation in breast cancer, we first used the UCSC Genome Browser (http://genome.ucsc.edu) and EBI CpGplot (http://www.ebi.ac.uk/Tools/seqstats/emboss_cpgplot/) to analyze the CYP1B1-AS1 promoter (2000 bp upstream), and no CpG islands, which are considered as the best predictors for defining active or potentially active promoter regions [16], were found (Fig. S2a, b). The gene discussed is PTGDR; the disease is breast cancer.