Ribociclib, also known as LEE011, is an orally available cyclin-dependent kinase (CDK) inhibitor targeting cyclin D1/CDK4 and cyclin D3/CDK6 cell cycle pathway, with potential antineoplastic activity. CDK4/6 inhibitor LEE011 specifically inhibits CDK4 and 6, thereby inhibiting retinoblastoma (Rb) protein phosphorylation. Inhibition of Rb phosphorylation prevents CDK-mediated G1-S phase transition, thereby arresting the cell cycle in the G1 phase, suppressing DNA synthesis and inhibiting cancer cell growth. Overexpression of CDK4/6, as seen in certain types of cancer, causes cell cycle deregulation. Ribociclib is in phase III clinical trials by Novartis for the treatment of postmenopausal women with advanced breast cancer. Phase II clinical trials are also in development for the treatment of liposarcoma, ovarian cancer, fallopian tube cancer, peritoneum cancer, endometrial cancer, and gastrointestinal cancer. Preregistration for Breast cancer (First-line therapy, Combination therapy, Late-stage disease) in the USA (PO) in November 2016.