RARB and cancer: In addition, it has been demonstrated that caffeic acid inhibited in vitro enzymatic DNA methylation and that the treatment of MCF-7 and MDA-MB-231 breast cancer cells with caffeic or chlorogenic acid partially inhibited the methylation of the promoter region of the RARB (retinoic acid receptor beta) gene, suggesting that propolis chemical compounds may function as epigenetic modulators in cancer cells [28].