HDAC1 has been identified as a direct negative regulator of cyclin-dependent kinase inhibitors (CDKI) such as p21 to promote unrestricted cell proliferation and cell cycle override in human tumor cells (Lagger et al. 2003) and mouse ES cells (Lagger et al. 2002; Zupkovitz et al. 2010). Here, HDAC1 is linked to neoplasm.