CDKN2A and cancer: When transplanted subcutaneously into immunodeficient hosts, p18Ink4c-suppressed p16Ink4a/Arf−/− astrocytes formed malignant tumors that were strongly Nestin-positive, in contrast to controlled p16Ink4a/Arf−/− astrocytes which were not tumorigenic in vivo (Figures 4B and 4C).