ATR and neoplasm: The shortening of telomeres can exert a tumor‐suppressive effect through the proliferation arrest induced by activating the kinases ATM (ATM Serine/Threonine Kinase) and ATR (ATR Serine/Threonine Kinase) at unprotected chromosome ends, while loss of telomere protection can lead to telomere crisis, which is a state of extensive genome instability that can promote cancer progression (Maciejowski & de Lange, 2017).