CDKN1B and posterior cortical atrophy: Cell surface HER2 is increased by independent methods of quiescence induction and is correlated with p27 levels. Using flow cytometry, we found that HER2 was expressed on the cell surface of all PCa cell lines analyzed: PC3, DU145, C4-2B, and LNCaP, as well as the benign prostate epithelial cell line, PNT2 – visualized by higher labeling as compared to an isotype control antibody (Fig. 2A).