HIPK2 and neoplasm: HIPK2’s function as a tumor suppressor has been supported by several pieces of evidence, including the HIPK2 pro-apoptotic and growth-arresting activities through p53-dependent and -independent mechanisms [19,20,21,22,23,24,25,26], the observation that the Hipk2 gene works as a haploinsufficient tumor suppressor in mice [27], and the identification of a few mechanisms of HIPK2 inactivation in human cancers, such as reduced expression and loss of heterozygosity [28,29,30,31].