Figure 1.

Deranged tissue homeostasis in hyperplastic tumors. (A) Under physiological conditions, the size of a specialized tissue is kept constant (beige cells). Tissue homeostasis is a steady state where tissue generation by cell proliferation (blue arrow on the left) and clearance of damaged or old cells by apoptosis or cellular senescence (blue arrow on the right) are kept in balance. (B) High levels of growth factors or the activation of oncogenes lead to hyperproliferation (enlarged blue arrow on the left), and loss of tumor suppressors cause reduced apoptosis or cellular senescence (narrowed blue arrow on the right). This dysfunctional tissue homeostasis evokes excessive tissue formation and hyperplastic tumor growth (grey cells).