DNA methylation profiling of 21 CpG sites in four genes, comprising six CpG sites in the RASSF1 gene and five CpG sites in each of the PTEN, CDH1 and PAX1 genes was performed by pyrosequencing on the four different tissue types—healthy ovarian tissues, benign OT, OC and BC-OC, and also on the corresponding plasma samples. This evidence concerns the gene PTEN and breast cancer.