SKP2 and neoplasm: Xenograft tumors derived from Skp2-knockout HCT116 cells were treated with irradiation and exhibited a significant decrease in tumor growth, tumor mass, and tumor cell proliferation compared to tumors derived from Skp2-knockout cells that did not receive the irradiation or to tumors retaining Skp2 and treated with irradiation (Fig. 1H–J).