Milciclib (PHA-848125) is a selective cyclin-dependent kinase (CDK) inhibitor primarily investigated for its potential in cancer therapy. It targets CDK2, CDK4, and CDK6, which play critical roles in cell cycle regulation, making it a candidate for disrupting uncontrolled cell proliferation in tumors. It has shown activity in preclinical models of various solid tumors and hematologic malignancies, including small cell lung cancer and neuroendocrine tumors. Due to its ability to cross the blood-brain barrier, milciclib has also been explored in brain tumor research and central nervous system malignancies. Clinical development has focused on evaluating its efficacy and safety in phase I and II trials, particularly in combination with other anticancer agents. Additionally, its mechanism supports investigation in diseases involving aberrant cell cycle control beyond oncology, though cancer remains the primary therapeutic focus.