# Palbociclib

Source: https://onco.cc/drugs/palbociclib/  
OnCo record `palbociclib` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Palbociclib was the first CDK4/6 inhibitor (2015), and in 2026 became the first approved as maintenance in HER2-positive, hormone-positive breast cancer.

## Summary

Palbociclib is a reversible CDK4/6 inhibitor that halts the cell cycle at G1, given as 125 mg daily for 21 days of a 28-day cycle with an aromatase inhibitor or fulvestrant. It was the first CDK4/6 inhibitor, approved in 2015 for HR-positive, HER2-negative advanced breast cancer on PALOMA-2 and PALOMA-3, which improved progression-free but not overall survival; the adjuvant trials PALLAS and PENELOPE-B were negative. In PATINA (SABCS 2024; approved Q2 2026) adding palbociclib to anti-HER2 plus endocrine maintenance in HR-positive, HER2-positive metastatic disease extended progression-free survival by about 15 months. Pfizer markets it; neutropenia (80%) is frequent but rarely febrile. Why it lacks the survival benefit seen with ribociclib and abemaciclib is debated. For a newcomer: the drug that opened the CDK4/6 class, now finding a new home in HER2-positive disease.

## Fields

- Kind: Treatment
- Status: approved
- Last checked: 2026-09-04
- Brand: Ibrance
- Modality: Small-molecule CDK4/6 inhibitor
- Mechanism: Reversible CDK4/6 inhibitor.
- Approvals: US 2015: HR+/HER2- advanced breast cancer with endocrine therapy; US 2026: HR+/HER2+ advanced breast cancer maintenance with anti-HER2 and endocrine therapy
- Dosing: Oral; 125 mg once daily for 21 days, then 7 days off (28-day cycle), with aromatase inhibitor or fulvestrant
- Toxicity (grade 3+): Neutropenia 66%; Infections 7%; Leukopenia 25%; Fatigue 2%; Nausea 1%; Stomatitis 1%; Diarrhoea 1%; Anaemia 6%; Rash 1%

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Palbociclib
- FDA label (DailyMed): https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Palbociclib

## Connected records

- biomarkers: [ER status (oestrogen receptor by IHC)](https://onco.cc/biomarkers/er-status/), [PR status (progesterone receptor by IHC)](https://onco.cc/biomarkers/pr-status/)
- cancers: [Acral melanoma](https://onco.cc/cancers/acral-melanoma/), [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Invasive lobular carcinoma of the breast](https://onco.cc/cancers/invasive-lobular-carcinoma/), [Male breast cancer](https://onco.cc/cancers/male-breast-cancer/)
- technologies: [CDK4/6 inhibitors](https://onco.cc/technologies/cdk46-inhibitor/), [St John's wort: an interaction to avoid](https://onco.cc/technologies/st-johns-wort-interaction/)
- targets: [CDK4/6](https://onco.cc/targets/cdk4-6/)
- companies: [Austrian Breast & Colorectal Cancer Study Group](https://onco.cc/companies/abcsg/), [GEICAM Spanish Breast Cancer Group](https://onco.cc/companies/geicam/), [Pfizer (incl. Seagen)](https://onco.cc/companies/pfizer/), [SOLTI Cancer Research Group](https://onco.cc/companies/solti/)
- trials: [A Comparative Study of AZD9833 Plus Palbociclib Versus Anastrozole Plus Palbociclib in Patients With ER-Positive HER2 Negative Breast Cancer Who Have Not Received Any Systemic Treatment for Advanced Disease](https://onco.cc/trials/nct04711252/), [A First-in-human Dose Escalation and Expansion Study to Evaluate the Safety, and Tolerability of AZD8421 Alone or in Combination in Participants With ](https://onco.cc/trials/nct06188520/), [A Phase Ib/II Study to Evaluate Multiple Combination Therapies of FWD1802 in Patients With ER+/HER2- BC](https://onco.cc/trials/nct07002177/), [A Study of Belzutifan (MK-6482) in Combination With Palbociclib Versus Belzutifan Monotherapy in Participants With Advanced Renal Cell Carcinoma (MK-6](https://onco.cc/trials/nct05468697/), [A Study to Evaluate Efficacy and Safety of Giredestrant Compared With Fulvestrant (Plus a CDK4/6 Inhibitor), in Participants With ER-Positive, HER2-Negative Advanced Breast Cancer Resistant to Adjuvant Endocrine Therapy (pionERA Breast Cancer)](https://onco.cc/trials/nct06065748/), [Capivasertib + CDK4/6i + Fulvestrant for Advanced/Metastatic HR+/HER2- Breast Cancer (CAPItello-292)](https://onco.cc/trials/nct04862663/), [Cyclin dEpendent Kinase in tRiple nEGatIVe brEast canceR - a "Window of Opportunity" Study](https://onco.cc/trials/nct05067530/), [DNA-guided Second Line Adjuvant Therapy for High Residual Risk, Estrogen Receptor Positive, HER-2 Negative Breast Cancer (DARE)](https://onco.cc/trials/nct04567420/), [First-in-Human Study of Tersolisib (STX-478) as Monotherapy and in Combination With Other Antineoplastic Agents in Participants With Advanced Solid Tumors](https://onco.cc/trials/nct05768139/), [Gedatolisib Plus Fulvestrant With or Without Palbociclib vs Standard-of-Care for the Treatment of Patients With Advanced or Metastatic HR+/HER2- Breast Cancer (VIKTORIA-1)](https://onco.cc/trials/nct05501886/), [INAVO120](https://onco.cc/trials/inavo120/), [Lung-MAP (SWOG S1400 and S1900)](https://onco.cc/trials/lung-map/), [Molecular Profiling of Advanced Soft-tissue Sarcomas](https://onco.cc/trials/nct03784014/), [National Lung Matrix Trial](https://onco.cc/trials/national-lung-matrix-trial/), [NCI-COG Pediatric MATCH (APEC1621)](https://onco.cc/trials/pediatric-match/), [NCI-MATCH (EAY131)](https://onco.cc/trials/nci-match/), [Open-Label Umbrella Study To Evaluate Safety And Efficacy Of Elacestrant In Various Combination In Participants With Metastatic Breast Cancer](https://onco.cc/trials/nct05563220/), [PALLAS & PENELOPE-B](https://onco.cc/trials/pallas-penelope-b/), [PALOMA-2](https://onco.cc/trials/paloma-2/), [PATINA](https://onco.cc/trials/patina/), [PENELOPE-B](https://onco.cc/trials/penelope-b/), [persevERA](https://onco.cc/trials/persevera/), [PF-07104091 as a Single Agent and in Combination Therapy](https://onco.cc/trials/nct04553133/), [Phase 3 Study of Gedatolisib as First-Line Treatment for Patients With HR-Positive, HER2-Negative Advanced Breast Cancer (VIKTORIA-2)](https://onco.cc/trials/nct06757634/), [Saruparib (AZD5305) Plus Camizestrant or Plus Endocrine Therapy, Compared With CDK4/6 Inhibitor Plus Endocrine Therapy or Plus Camizestrant in HR-Positive, HER2-Negative (IHC 0, 1+, 2+/ ISH Non-amplified), BRCA1, BRCA2, or PALB2m Advanced Breast Cancer](https://onco.cc/trials/nct06380751/), [SNV4818 in Participants With Advanced Solid Tumors](https://onco.cc/trials/nct06736704/), [Study for Participants Continuing From Pfizer-sponsored Palbociclib (a Study Medicine) Studies](https://onco.cc/trials/nct05226871/), [Study of AVZO-021 in Patients With Advanced Solid Tumors](https://onco.cc/trials/nct05867251/), [Study Of Palbociclib Combined With Chemotherapy In Pediatric Patients With Recurrent/Refractory Solid Tumors](https://onco.cc/trials/nct03709680/), [Study of PF-07220060 With Letrozole in Adults With HR-positive HER2-negative Breast Cancer Who Have Not Received Anticancer Treatment for Advanced/Metastatic Disease](https://onco.cc/trials/nct06760637/), [Study of PF-07248144 in Advanced or Metastatic Solid Tumors](https://onco.cc/trials/nct04606446/), [Study to Investigate Outcome of Individualized Treatment in Patients With Metastatic Colorectal Cancer](https://onco.cc/trials/nct05725200/), [TAPUR (Targeted Agent and Profiling Utilization Registry)](https://onco.cc/trials/tapur/), [Vepdegestrant (ARV-471/PF-07850327) + Palbociclib vs Letrozole + Palbociclib in ER(+)/HER2(-) Advanced Breast Cancer](https://onco.cc/trials/nct05909397/)
- people: [Angela DeMichele](https://onco.cc/people/angela-demichele/), [Dennis J. Slamon](https://onco.cc/people/dennis-slamon/), [Hope S. Rugo](https://onco.cc/people/hope-rugo/), [Komal Jhaveri](https://onco.cc/people/komal-jhaveri/), [Massimo Cristofanilli](https://onco.cc/people/massimo-cristofanilli/), [Miguel Martín](https://onco.cc/people/miguel-martin/), [Richard S. Finn](https://onco.cc/people/richard-finn/), [Seock-Ah Im](https://onco.cc/people/im-seock-ah/), [Sherry Lansing](https://onco.cc/people/sherry-lansing/), [Yeon Hee Park](https://onco.cc/people/park-yeon-hee/)
- ideas: [CDK4-selective inhibitors as the new first-line backbone](https://onco.cc/ideas/idea-cdk4-selective-first-line/), [Payers fund trials of cheaper, shorter or lower-dose versions of expensive treatments](https://onco.cc/ideas/idea-fund-payer-funded-pragmatic-trials/), [Pharmacist interaction check before every oral cancer-drug prescription](https://onco.cc/ideas/idea-acc-pharmacist-interaction-review-oral-anticancer/)
- institutions: [Comprehensive Cancer Center Vienna, Medical University of Vienna / AKH](https://onco.cc/institutions/ccc-vienna/), [Instituto Alexander Fleming](https://onco.cc/institutions/instituto-alexander-fleming/), [UCLA Jonsson Comprehensive Cancer Center](https://onco.cc/institutions/ucla-jonsson/)
- pathways: [Breast cancer (KEGG map)](https://onco.cc/pathways/breast-cancer-signalling/), [Oestrogen receptor signalling](https://onco.cc/pathways/er-signaling/), [p53 / RB / cell-cycle checkpoint](https://onco.cc/pathways/p53-cell-cycle/), [The cell-cycle engine (cyclins & CDKs)](https://onco.cc/pathways/cell-cycle-engine-cdks/)
- pairings: [CDK4/6 inhibitor + endocrine therapy](https://onco.cc/pairings/cdk46-plus-endocrine/)
- terms: [Cell cycle](https://onco.cc/terms/cell-cycle/), [Hallmarks of cancer as a synthesis of the theories](https://onco.cc/terms/hallmarks-synthesis/), [Hormone therapy](https://onco.cc/terms/hormone-therapy/), [Inhibitor](https://onco.cc/terms/inhibitor/)
- roadmaps: [Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test](https://onco.cc/roadmaps/hormonal-therapy-roadmap/)

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JSON: https://onco.cc/api/v1/entities/palbociclib.json