CDKN1B and neoplasm: Quiescent cells typically express lower levels of Rb-E2F pathway activators (e.g., CycD, Cdk2) and higher levels of, p27Kip1, a Cdk inhibitor, and Mirk/DYRK1B, a cell cycle serine/threonine kinase which both play a role in increased tumor aggressiveness and poor patient outcome21–25.