CDKN2A and neoplasm: By qPCR analysis, elevated expression levels of Ink4/ARF (encoding p16Ink4a, p15Ink4b, p19Arf) and p21, both of which encode senescence-mediating proteins, were detected in the tumor (GFP+) cells compared with the surrounding parenchyma (GFP−) cells (Fig. 1c).