It has been previously documented that in breast cancer MCF-7 cells treated with 5Aza-dC (0.6 μM, for 96 h) a significant decrease in promoter methylation of tumour suppressor genes, i.e., APC (Adenomateus polyposis coli), PTEN (Phosphate and TENsin homologue) and RARβ2 (retinoic acid receptor β2), is observed. This evidence concerns the gene PTEN and breast carcinoma.