MDM4 and neoplasm: Moreover, amplification of TP53 inhibitory proteins MDM2 (12q15) and MDM4 (1q32) and deletion of the MDM2 inhibitor ARF (CDKN2A, 9p21) exhibited a trend for being associated with high numbers of subclonal mutations in 8 tumor types (p value < 0.1, S2 Table).