PCNA and neoplasm: When MSCs are injected at the tumor site in vivo, they stimulate tumor growth and support metastasis, or inhibit tumorigenesis by antitumor effects involving downregulation of Akt, beta-catenin, Bcl-2, c-Myc, proliferating cell nuclear antigen and surviving, leading to reduced proliferation, G1 arrest, suppression of oncogenes and increased apoptosis (Klopp et al., 2011).