Thus, contact inhibition of proliferation may be viewed as a reversible form of cell cycle arrest. Furthermore, to transition from cell cycle arrest to senescence, contact-inhibited cells must activate growth-activating pathways such as mTOR. Once cells in high-density cultures become confluent enough such that the cell area falls below a critical value, the adhesion formations trigger pathways that downregulate mitogen signaling and cell proliferation.
Contact inhibition of cell proliferation can be seen as a reversible form of cell cycle arrest.  To progress from cell cycle arrest to senescence, contact-inhibited cells must activate growth-promoting pathways like mTOR. When cells in high-density cultures become densely packed, the adhesion formations trigger pathways that reduce mitogen signaling and cell division.