Regardless, caffeic acid phenethyl ester (CAPE) currently seems to be the most interesting component isolated from propolis and is currently being developed as a potential anti-cancer drug since it can inhibit the in vitro growth of many cell lines [17] including the estrogen receptor positive (ER+) and negative (ER-) MCF7 and MDA231 cell lines, respectively [18], along with the chemoresistant PANC-1 cell line [19]. This evidence concerns the gene ESR1 and cancer.