ERBB2 and breast cancer: To further support this speculation, the human HER2 + BC cell lines HCC1569, MDAMB361, EFM192A and HCC1954, which have different susceptibilities to lapatinib treatment (Supplementary Figure S2), were grown in vitro in monolayer in the presence of fetal bovine serum (FBS) containing FAs (FBS—FA +) or not (FBS—FA-) for 24 h, 48 h and 72 h, and then the percentage of CD44High/CD24Low cells was assessed via flow cytometry.