palbociclib
Ibrance (palbociclib) is an oral CDK4/6 inhibitor from Pfizer for hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. Combined with endocrine therapy, it blocks the cell-cycle machinery cancer cells use to multiply, slowing or stopping tumour growth.
This page is based on FDA prescribing information and the EMA medicine record for palbociclib, cross-checked with MedlinePlus and the National Cancer Institute dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
A cancer cell is a factory stuck with the divide button pressed down, and CDK4/6 are the two switches that keep it running. Palbociclib flips both switches off. The factory freezes at the quality checkpoint before copying its DNA, so no new cancer cells come off the line while normal cells with other controls can still get through.
In simple terms
Cancer cells multiply by cycling through growth and division, and many breast cancers lean heavily on the enzymes CDK4 and CDK6 to keep that cycle turning. Palbociclib, taken by mouth, selectively inhibits CDK4 and CDK6, which stops the phosphorylation of the retinoblastoma protein and arrests cells early in the G1 phase. DNA replication is suppressed and tumour cell proliferation slows. Given with endocrine therapy, it helps control hormone receptor-positive, HER2-negative advanced breast cancer.
In depth
Palbociclib is an orally available cyclin-dependent kinase inhibitor that selectively inhibits CDK4 and CDK6, thereby blocking retinoblastoma (Rb) protein phosphorylation early in the G1 phase and inducing cell cycle arrest. This suppresses DNA replication and decreases tumour cell proliferation. CDK4 and CDK6 are serine/threonine kinases that are upregulated in many tumour cell types and play a key role in regulating cell cycle progression, which underlies the drug's use with aromatase inhibitors, fulvestrant, and other partners across breast cancer settings.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
How palbociclib blocks CDK4/6 and arrests the cell cycle in G1
- Palbociclib is an orally available cyclin-dependent kinase inhibitor that selectively inhibits CDK4 and CDK6, thereby blocking retinoblastoma (Rb) protein phosphorylation early in the G1 phase and inducing cell cycle arrest.
- This suppresses DNA replication and decreases tumour cell proliferation.
- CDK4 and CDK6 are serine/threonine kinases that are upregulated in many tumour cell types and play a key role in regulating cell cycle progression, which underlies the drug's use with aromatase inhibitors, fulvestrant, and other partners across breast cancer settings.
- Given with endocrine therapy, it helps control hormone receptor-positive, HER2-negative advanced breast cancer.
Target: Cyclin-dependent kinases 4 and 6 (CDK4, CDK6)
Serine/threonine kinases that push cells past the early checkpoint of the division cycle; many cancers upregulate them to keep multiplying, so blocking them stalls the cell cycle.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- In combination with an aromatase inhibitor as initial endocrine-based therapy, or with fulvestrant in patients with disease progression following endocrine therapy, for the treatment of adults with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer
- In combination with inavolisib and fulvestrant, for the treatment of adults with endocrine-resistant, PIK3CA-mutated, HR-positive, HER2-negative, locally advanced or metastatic breast cancer, as detected by an FDA-authorized test, following recurrence on or after completing adjuvant endocrine therapy
- In combination with trastuzumab, with or without pertuzumab, and endocrine therapy, for the maintenance treatment of adults with HR-positive, HER2-positive locally advanced or metastatic breast cancer following induction treatment
Approved uses in European Union
EMA- In combination with an aromatase inhibitor, for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer
- In combination with fulvestrant, for the treatment of hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer in women who have received prior endocrine therapy, with endocrine therapy combined with a luteinizing hormone releasing hormone (LHRH) agonist in pre- or perimenopausal women
Official sources
The statements on this page trace back to these records.
- Ibrance (palbociclib) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- U.S. Food and Drug Administration: palbociclib prescribing information
U.S. Food and Drug Administration
- MedlinePlus: palbociclib
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: palbociclib
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.