Palbociclib is an investigational drug currently being evaluated for the treatment of breast cancer. Palbociclib is an oral and selective inhibitor of cyclin dependent kinases (CDK) 4 and 6. It may work by inhibiting cell growth and DNA replication.

Palbociclib has received Breakthrough Therapy designation by the United States Food and Drug Administration (FDA) for the potential treatment of patients with breast cancer.

Pfizer has initiated a randomized, multi-center, double-blind Phase 3 study (known as Study 1008) evaluating palbociclib in combination with letrozole versus letrozole alone as a first-line treatment for post-menopausal patients with ER+, HER2- locally advanced or metastatic breast cancer.

In addition to breast cancer, palbociclib is being investigated for the treatment of other cancers.