CDKN1B and cancer: It also regulates the cell cycle regulators p27kip1 and p57kip2, which are essential for cell-cell contact inhibition in healthy tissue but are lost or disrupted in cancer cells, primarily due to the loss of E-cadherin in cancer cells (Croix et al., 1998; Cavallaro and Christofori, 2004a; Migita et al., 2008).