Finally, when considering that (1) >10 billion normal cells need to be replaced every day55,56 and (2) CDK4/6 inhibitors do not have toxicity issues common among other CDK inhibitors (the side effects of CDK4/6i are primarily hematopoietic)57, the use of this alternate mechanism may explain why most normal tissues tolerate CDK4/6 inhibitors during cancer therapy. The gene discussed is CDK4; the disease is cancer.