NPM1 and neoplasm: The notion that ARF acts independently of the Mdm2–p53 axis in tumor surveillance is in line with the observation that ARF interacts with a multitude of different cellular partners, such as proteins involved in transcriptional control (E2Fs, DP1, p63, c-Myc, Hif1α), nucleolar proteins such as nucleophosmin (NPM/B23), viral proteins (HIV-1Tat), mitochondrial protein (p32) and others [10,57].