Small-molecule inhibitors of the closely related cyclin-dependent kinases 4 and 6 (CDK4/6 is) that have shown success in treating patients with metastatic breast cancer have been only modestly effective against other tumor types. A research team from the Icahn School of Medicine at Mount Sinai recently found a biological rationale for that disparity, which could bode well for the development of targeted therapies across a wide range of cancers. The results were described in Nature Cancer in March 2021.