CDKN1B and neoplasm: Constitutive activation of RTKs induces expression and/or phosphorylation of a variety of intracellular proteins involved in cell survival, proliferation, and motility and adhesion signals, including components of the PTEN/PI3K/AKT pathway [4], which modulates cell cycle progression by down-regulation of p27Kip1 in various neoplasms.