is an oral cell cycle protein kinase dependent CDK4/6 inhibitor, in HR +, HER2 breast cancer cells, CDK4 and CDK6 promotes retinoblastoma protein phosphorylation (retinoblastomaprotChemicalbookein, Rb), And promote cell cycle progression and cell proliferation. Abemaciclib inhibits the phosphorylation of Rb and blocks the progression of cells from the G1 phase of the cell cycle to the S phase, leading to cell senescence and apoptosis. New drug for breast cancer