Palbociclib (codenamed PD-0332991, trade name Ibrance) is a drug for the treatment of ER-positive and HER2-negative breast cancer developed by Pfizer. It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6.

ER+ breast cancer

The drug was reviewed and approved under the Food and Drug Administration’s (FDA) accelerated Priority Review and Breakthrough Therapy designation programs on February 3, 2015 as a treatment (in combination with letrozole) for patients with estrogen receptor positive advanced breast cancer. This was an accelerated approval.

A potentially confirmatory phase 3 trial, PALOMA-2, was fully enrolled by Feb 2015. The PALOMA-2 trial reported positive results in April 2016. The results of PALOMA-2 trial was published in November 2016 which showed significantly longer progression free survival in patients on palociclib in combination with letrozole compared to patients on letrozole alone. However addition of palciclib caused higher rates of myelotoxic events in the study

HR+ breast cancer

The PALOMA-3 trial announced in April 2015 that the addition of palbociclib was superior to fulvestrant alone for progression-free survival

In the phase 2 PALOMA-1 trial reported at the April 2014 annual meeting of the American Association for Cancer Research, the addition of palbociclib to letrozole was shown to significantly slow the progression of advanced cancer (median progression-free survival increased from 10.2 months to 20.2 months), but was not shown to have a statistically significant effect on increasing patients' overall survival times.

Ibrance "can be ordered through select" specialty pharmacies and "sells for $9,850 for 30 days or $118,200 for a year's supply before discounts. According to a statement by the New York-based Pfizer the price "is not the cost that most patients or payors pay" since most prescriptions are dispensed through health plans, which negotiate discounts for medicines or get government-mandated price concessions. In the United States specialty pharmacies fill prescriptions for drugs that are usually high cost.