PPIB and breast cancer: In agreement with MCF-7 breast cancer cells, but in contrast to melanoma cells, the expression of breast epithelium-specific and epithelial-specific markers, such as β-casein, α-lactalbumin, epithelial membrane antigen (EMA), and keratin-19 as well as the induction of β-casein expression and production of milk lipids by β-heregulin and vitamin E was clearly observed in MDA-MB-435 cells [38].