LY2835219 is a selective inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), which play a key role in regulating the cell cycle. It is primarily investigated for its antitumor activity, especially in cancers driven by dysregulation of the retinoblastoma (Rb) pathway, such as certain breast cancers, glioblastoma, and other solid tumors. By inhibiting CDK4/6, LY2835219 blocks the phosphorylation of the Rb protein, leading to cell cycle arrest in the G1 phase and suppression of uncontrolled cell proliferation. In clinical and preclinical studies, LY2835219 has shown promise in combination with other anticancer agents, including hormone therapies and targeted drugs, to enhance tumor response and overcome resistance. Its ability to cross the blood-brain barrier also makes it a candidate for treating brain tumors and central nervous system metastases. Research continues to explore optimal dosing, long-term efficacy, and safety in various cancer types.