NR4A1 and breast cancer: However, pan‐CDK inhibitors are not widely used due to their dose‐limiting toxicities.[25] Currently, the new generation of CDK4/6 inhibitors (palbociclib, abemaciclib, and ribociclib) have become broadly used cancer therapeutics.[26] After the striking success of combining CDK4/6 inhibitors and the hormone receptor antagonist letrozole for breast cancer treatment, many other CDK4/6 inhibitors are being evaluated in ongoing clinical trials.[27] Thus, the underlying mechanism of the antitumorigenic effects of CDK4/6 inhibitors needs to be determined.