Despite that various breast cancer cell lines displayed differential methylation levels at the RARRES1 promoter (Figure 3A), they all retained similar degrees of methylation at the constitutive hypermethylated locus know as LINE-1 (Long Interspersed Nucleotide Element 1) serving as a positive control for global methylation [19] (Figure S1). This evidence concerns the gene RARRES1 and breast cancer.