RB1 and leukemia: The Cyclin D1‐CDK4/6 complex phosphorylates RB1 and CDK4/6 inhibitors have been used to treat ER+ HER2‐ breast cancer, but not BLBC.[3] Because the CDK4/6 inhibitor and the XPO1 inhibitor target a common protein RB1 and they have shown positive therapeutic effects in liver cancer and leukemia,[44, 45] we predict that the combination of the two drugs will be effective in RB1 positive BLBC.