ERBB2 and breast cancer: Anticancer activity of two pentacyclic triterpenoids, ursolic acid (UA) and betulinic acid (BA), against three breast cancer cells of different receptor status, namely MCF-7 (ER+, PR+/−, HER2−), MDA-MB-231 (ER−, PR−, HER2−) and SK-BR-3 (ER−, PR−, HER2+) was compared and a biphasic response was revealed (Fig. 9).