Here, we applied aqueous extracts from two Taraxacum species, T. mongolicum and T. formosanum, to compare their potential antitumor effects against three human breast cancer cell lines: MDA-MB-231 (ER−, PR−, and HER2−), ZR-75-1 (ER+, PR+/−, and HER2−), and MCF-7 (ER+, PR+, and HER2−). Here, ERBB2 is linked to breast cancer.