PERP and breast carcinoma: Indeed, on examining Perp expression in normal mammary cells and breast cancer cell lines, we found that Perp levels were reduced in the majority of the human breast cancer cell lines tested, relative to the robust Perp levels observed in untransformed human and mouse breast epithelial cell lines (MCF10A and EpH4, respectively) [36] and primary mouse mammary epithelial cells (data not shown; Figure 4).