Key points
- Palbociclib is a targeted tablet that is always taken with a hormone medicine (such as letrozole or fulvestrant) [1].
- In a large study, adding palbociclib to letrozole kept the disease under control for longer [1, 2].
- It is used in advanced hormone receptor-positive breast cancer, and has recently been approved for some HER2-positive patients alongside anti-HER2 drugs [1, 3].
- The most common side effect is a drop in white blood cells, which happens in most patients; this is why regular blood tests are needed [1].
- Once a day for 21 days in a row, then 7 days off; with or without food. Do not eat grapefruit during treatment [1].
What is this drug and how does it work?
For physicians
Palbociclib, brand name Ibrance, is a "kinase inhibitor" that blocks the enzymes cyclin-dependent kinases 4 and 6 (CDK4/6) [1]. Cyclin D1 and the CDK4/6 enzymes sit in pathways that lead to cell proliferation. In laboratory studies, palbociclib reduced the proliferation of oestrogen receptor-positive breast cancer cells by stopping cells from moving from the G1 phase to the S phase of the cell cycle [1].
Combining palbociclib with anti-oestrogen drugs reduces phosphorylation of the retinoblastoma (Rb) protein and increases growth arrest compared with either drug alone [1]; this is why palbociclib is always used with hormone therapy. It was first approved in the United States in 2015 [1].
Which cancers is it used for?
Your doctor may prescribe this drug for:
- Advanced or spread hormone receptor-positive, HER2-negative breast cancer [1]
- Advanced hormone receptor-positive, HER2-negative breast cancer with a PIK3CA mutation [1, 6]
- Advanced or spread hormone receptor-positive, HER2-positive breast cancer [1, 3]
Whether it suits you depends on the type and stage of your cancer and your test results. Details of each use are in the section for doctors.
For physicians
| Cancer | Treatment setting |
|---|---|
| HR-positive / HER2-negative advanced or metastatic breast cancer | With an aromatase inhibitor as initial endocrine-based therapy [1] |
| HR-positive / HER2-negative advanced or metastatic breast cancer | With fulvestrant after disease progression on endocrine therapy (pre- and postmenopausal women) [1] |
| HR-positive / HER2-negative advanced breast cancer with a PIK3CA mutation | With inavolisib and fulvestrant in endocrine-resistant disease that recurred during or after completing adjuvant endocrine therapy [1, 6] |
| HR-positive / HER2-positive advanced or metastatic breast cancer | Maintenance with trastuzumab (with or without pertuzumab) and endocrine therapy, after induction chemotherapy [1, 3] |
All approved uses of palbociclib are for advanced or metastatic disease [1].
| Cancer | Key evidence |
|---|---|
| HR-positive / HER2-negative advanced or metastatic breast cancer | PALOMA-2 (666 postmenopausal women): median progression-free survival 24.8 vs 14.5 months (HR 0.576); the difference in overall survival was not statistically significant [1, 2] |
| HR-positive / HER2-negative advanced or metastatic breast cancer | PALOMA-3 (521 patients): median progression-free survival 9.5 vs 4.6 months (HR 0.461); median overall survival 34.9 vs 28.0 months, not statistically significant [1, 4, 5] |
| HR-positive / HER2-negative advanced breast cancer with a PIK3CA mutation | INAVO120 (325 patients): adding inavolisib to palbociclib and fulvestrant increased median progression-free survival from 7.3 to 15.0 months (HR 0.43) [1, 6] |
| HR-positive / HER2-positive advanced or metastatic breast cancer | PATINA (518 patients): median progression-free survival 44.3 vs 29.1 months (HR 0.75) [1, 3] |
HR: hazard ratio; a value below 1 means a lower risk of disease progression or death.
How it is taken and dose
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Treatment regimens and doses: index4 regimens
Palbociclib is an oral tablet taken once a day, at about the same time each day, for 21 days in a row, followed by 7 days off; these 28 days make one treatment cycle [1]. You can take the tablet with or without food, but swallow it whole; do not chew, crush or split it, and do not take a broken or cracked tablet [1].
If you miss a dose or vomit after taking the tablet, do not take an extra dose; take the next dose at your usual time [1]. Palbociclib is prescribed with a hormone medicine, and women who are premenopausal or going through the menopause also need a medicine that suppresses ovarian function (an LHRH agonist) [1]. In the studies, treatment continued until the disease progressed or side effects became intolerable [1]. Never change the dose on your own or stop the medicine without talking to your doctor.
Dose levels: 125 → 100 → 75 mg a day; if less than 75 mg is needed, stop [1].
Dose adjustment [1]:
- Grade 3 neutropenia on day 1 of a cycle: hold and repeat the CBC within a week; on recovery to grade 2 or lower, start the next cycle at the same dose. Grade 3 on day 15 of the first two cycles: continue to the end of the cycle and check the CBC on day 22 (if grade 4, manage as grade 4). With prolonged recovery (more than a week) or recurrent grade 3 on day 1 of cycles, consider a dose reduction.
- Grade 3 neutropenia with a temperature of 38.5 °C or higher and/or infection, or grade 4: hold until grade 2 or lower and resume at the next lower level.
- Persistent grade 3 or higher non-haematological toxicity despite treatment: hold until grade 1 or lower (or grade 2 if not a safety risk) and resume at the next lower level. Severe ILD/pneumonitis: stop permanently.
LHRH agonist: with the aromatase inhibitor or fulvestrant regimens, pre- or perimenopausal women should receive a concurrent LHRH agonist; in men, consider an LHRH agonist [1].
Interactions: avoid strong CYP3A inhibitors and grapefruit; if unavoidable, use 75 mg once daily and, after the inhibitor is stopped (3 to 5 half-lives), return to the previous dose. Avoid strong CYP3A inducers. Sensitive CYP3A substrates with a narrow therapeutic window may need a dose reduction [1]. The drug names are in the section Interactions, pregnancy and precautions.
Kidney and liver: CrCl above 15 mL/min and Child-Pugh A and B: no adjustment; Child-Pugh C: 75 mg once daily (21 days on, 7 days off). Not studied in haemodialysis [1].
Monitoring: CBC before starting, at the start of each cycle and on day 15 of the first two cycles; if the maximum neutropenia in the first 6 cycles was grade 1 or 2, then every 3 months before the start of a cycle. Respiratory symptoms (ILD) [1].
For physicians
Standard doses (FDA label)
Palbociclib + aromatase inhibitor
HR-positive/HER2-negative advanced or metastatic breast cancer; initial endocrine-based therapyEach drug’s schedule in the table
HR-positive/HER2-negative advanced or metastatic breast cancer; initial endocrine-based therapy
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Palbociclib | 125 mg | Oral, with or without food, tablet swallowed whole | Once daily, days 1 to 21, every 28 days |
| Aromatase inhibitor (such as letrozole) | As in that drug's label | Oral | Daily, continuously |
Dose as in the FDA label [1].
Palbociclib + fulvestrant
The same disease, after progression on endocrine therapyCycle length: Every 28 days
The same disease, after progression on endocrine therapy
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Palbociclib | 125 mg | Oral, with or without food, tablet swallowed whole | Once daily, days 1 to 21 |
| Fulvestrant | As in that drug's label | Intramuscular injection | As in the label |
Dose as in the FDA label [1].
Inavolisib + palbociclib + fulvestrant (INAVO120)
HR-positive/HER2-negative advanced disease with a PIK3CA mutation, endocrine-resistant (recurrence during or after completing adjuvant endocrine therapy)Each drug’s schedule in the table
HR-positive/HER2-negative advanced disease with a PIK3CA mutation, endocrine-resistant (recurrence during or after completing adjuvant endocrine therapy)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Inavolisib | 9 mg | Oral | Once daily, continuously |
| Palbociclib | 125 mg | Oral, with or without food, tablet swallowed whole | Once daily, days 1 to 21, every 28 days |
| Fulvestrant | 500 mg | Intramuscular injection | Cycle 1: days 1 and 15; then day 1 every 28 days |
Schedule as described for the trial in the palbociclib label [1, 6]. Before starting inavolisib, check fasting glucose and HbA1c and optimise blood glucose; a missed inavolisib dose can be taken within 9 hours, after that it is skipped [7].
Evidence: INAVO120 (2024)
Maintenance palbociclib in HER2-positive disease (PATINA)
HR-positive/HER2-positive advanced or metastatic disease without progression after 4 to 8 cycles of a taxane + trastuzumab (with or without pertuzumab)Each drug’s schedule in the table
HR-positive/HER2-positive advanced or metastatic disease without progression after 4 to 8 cycles of a taxane + trastuzumab (with or without pertuzumab)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Palbociclib | 125 mg | Oral, with or without food, tablet swallowed whole | Once daily, days 1 to 21, every 28 days |
| Trastuzumab (± pertuzumab) | As in those drugs' labels | IV | Every 3 weeks |
| Endocrine therapy (fulvestrant or an aromatase inhibitor) | As in the label | — | — |
Evidence: PATINA (2026)
Doses follow the trial protocol, guideline or official drug label (source given in the notes of each regimen). Before prescribing, check blood counts, renal and hepatic function, drug interactions and the patient’s condition, and adjust the dose according to the drug label.
Side effects
For physicians
| Side effect | Frequency (all grades) | Grade 3 or 4 |
|---|---|---|
| Low neutrophils (neutropenia) | 80% | 56% grade 3, 10% grade 4 [1] |
| Infections (mostly upper respiratory and urinary infections) | 60% | 6% grade 3, 1% grade 4 [1] |
| Low white blood cells (leucopenia) | 39% | 24% grade 3, 1% grade 4 [1] |
| Tiredness | 37% | 2% [1] |
| Nausea | 35% | Less than 1% [1] |
| Hair loss | 33% | Grade 1 only (30%) and grade 2 (3%) [1] |
| Mouth inflammation and sores (stomatitis) | 30% | 1% [1] |
| Diarrhoea | 26% | 1% [1] |
| Anaemia | 24% | 5% grade 3 [1] |
| Skin rash | 18% | 1% [1] |
| Decreased appetite | 15% | 1% [1] |
Other important side effects with a frequency below 10%: nosebleeds (9%), watery eyes (6%), dry eyes (4.1%), blurred vision (3.6%) and febrile neutropenia (2.5%) [1].
Serious side effects
These side effects are less common but serious; if you notice any sign of them, tell your team early:
For physicians
The FDA label for palbociclib has no boxed warning, but lists these warnings and precautions [1]:
- Neutropenia: in PALOMA-2 and PALOMA-3, grade 3 or higher neutropenia occurred in 66% of patients; the median time to the first neutropenia was 15 days and the median duration of grade 3 or higher neutropenia was 7 days. Febrile neutropenia was reported in 1.8% of patients, and one death from neutropenic sepsis occurred in PALOMA-3 [1].
- Interstitial lung disease (ILD) and pneumonitis: in the PALOMA-1, -2 and -3 trials, 1% of patients developed ILD/pneumonitis of any severity (0.1% grade 3 or 4), with no fatal cases in these trials; but fatal cases have been reported after marketing [1].
- Embryo-fetal toxicity: based on animal studies and its mechanism of action, palbociclib can harm a fetus [1].
When should I call my doctor?
Contact your treatment team straight away if you have [1]:
- Any fever, chills or signs of infection (low white blood cells can make an infection dangerous)
- New or worsening shortness of breath, cough or chest pain
- Dizziness, severe weakness, or unusual bleeding or bruising
- A possible or confirmed pregnancy
Interactions, pregnancy and precautions
- Other medicines: some medicines, such as the antibiotic clarithromycin, antifungals (itraconazole, ketoconazole, voriconazole, posaconazole) and ritonavir, roughly double the amount of palbociclib in the blood and should not be taken with it [1]. The tuberculosis medicine rifampicin, epilepsy medicines (phenytoin, carbamazepine), enzalutamide and the herb St John's wort weaken it and should not be taken at the same time [1].
- Grapefruit: do not eat grapefruit or drink grapefruit juice during treatment [1].
- Palbociclib may raise the level of some sensitive medicines with a narrow therapeutic window (such as ciclosporin, tacrolimus, sirolimus, everolimus and fentanyl), so their dose may need adjusting [1].
- Pregnancy and contraception: a pregnancy test is needed before starting treatment. Women who could become pregnant should use effective contraception during treatment and for at least 3 weeks after the last dose; men whose partner could become pregnant should do so for 3 months after the last dose [1].
- Breastfeeding: do not breastfeed during treatment and for 3 weeks after the last dose [1].
- Male fertility: palbociclib may reduce male fertility; talk to your doctor about sperm banking before starting [1].
- Give your doctor and pharmacist a full list of your medicines, supplements and herbal products.
Frequently asked questions
Is palbociclib chemotherapy?
Why do I stop the medicine for one week every month?
The schedule of 21 days on and 7 days off is the approved schedule used in all the main studies [1]. Keep taking the accompanying hormone therapy on the days off, as your doctor has told you.
If my white blood cells drop, will treatment be stopped?
A drop in white blood cells is the most common side effect of palbociclib and is usually managed with a short pause, a delay in starting the next cycle or a lower dose; your doctor decides based on your blood tests [1]. Almost no one (about 1 in 100 patients) stopped the medicine for good because of low white blood cells [1].
Can I have grapefruit or herbal medicines?
Is palbociclib also given after surgery for early breast cancer?
According to the FDA label, the approved uses of palbociclib are only in advanced or metastatic breast cancer [1]. For high-risk early disease, talk to your doctor about other options (see the ribociclib and abemaciclib pages).
Scientific evidence
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Key studies
1 itemBreast Cancer, Version 4.2026, NCCN Clinical Practice Guidelines In Oncology
Related cancer types
References
7 referencesShow all references, 5 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2Palbociclib and Letrozole in Advanced Breast Cancer
- 3
- 4Palbociclib in Hormone-Receptor–Positive Advanced Breast Cancer
- 5Overall Survival with Palbociclib and Fulvestrant in Advanced Breast Cancer
- 6
- 7ITOVEBI (inavolisib) tablets, for oral use: Prescribing Information
This page is based on reputable scientific sources and was last updated on 27 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/drugs/palbociclib/