DNMT1 and breast cancer: It has been also suggested that SFN effect cannot be associated with reduction of mRNA expression of the DNMT1. This fact has been confirmed by studies in which changes in methylation and expression of selected tumour suppressor genes in MCF-7 breast cancer cells exposed to SFN at 10 μM concentration for 96 h have not been associated with any relevant effects on DNMT1 mRNA level [36].