RARB and breast cancer: Key targets of aberrant promoter hypermethylation in breast cancer development include genes involved in all stages of tumorigenesis such as DNA repair (BRCA1), receptors (ER, RAR-β), intracellular signalling pathways, cell cycle regulation (Cyclin D2, p16INK4A), transcription factors (Twist), adhesion molecules (E-cadherin) and apoptosis (HOXA5) [7-14].