Palbociclib is a piperazine pyridopyrimidine that acts in the cell cycle machinery. It is a second generation cyclin-dependent kinase inhibitor selected from a group of pyridopyrimidine compounds due to its favorable physical and pharmaceutical properties. Palbociclib was developed by Pfizer Inc after the discovery that identified the cyclin-dependent kinases as key regulators of cell growth. It was originally FDA approved on March 2015 for the treatment of HR-positive, HER2-negative advanced or metastatic breast cancer and its indications were updated in April 2019 to include male patients based on findings from postmarketing reports and electronic health records demonstrating safety and clinical efficacy.