CDK4 and breast cancer: Indeed, these CDK4/6 inhibitors have been shown to induce cellular senescence in many cancer types such as breast cancer (in vitro and in vivo), Ewing sarcoma (in vitro), and neuroblastoma (in vitro) [100, 101, 102, 103, 104, 105, 106], although in these studies senescence induction has mainly been judged by SA‐β‐galactosidase positivity, which can be an indicator of cellular senescence but is not an absolute marker solely because it is also known to be positive in some quiescent cells [107].