PICLIB 100 mg Capsules PICLIB contains Palbociclib, a selective inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6). It blocks the phosphorylation of retinoblastoma (Rb) protein, preventing G1-to-S phase cell cycle progression and inhibiting tumor cell proliferation. It is indicated for treating hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer in combination with an aromatase inhibitor as initial endocrine-based therapy or with fulvestrant following disease progression.