However, we found that in breast cancer cells the luciferase activity of a PREX1 promoter reporter that includes the Sp1 sites (located in the proximal CpG island, positions -201/-192 and -170/-161) does not change after methylation (data not shown), suggesting that methylation of the Sp1 sites is not relevant for controlling the expression of the gene. This evidence concerns the gene SP1 and breast cancer.