The short answer
Ibrance (Palbociclib) is a targeted therapy called a CDK4/6 inhibitor. It blocks proteins called CDK4 and CDK6 that control how fast cells divide, which can slow or stop the growth of some breast cancers. It is used for advanced or metastatic breast cancer that is hormone-receptor-positive, and is always combined with another treatment such as a hormone therapy. It is taken as capsules or tablets by mouth. Like all cancer medicines it can cause side effects; this page explains the common ones and the warning signs to report. It is educational only and not a substitute for your care team's advice.
Ibrance is the brand name; its generic name is palbociclib.
It is a targeted therapy called a CDK4/6 inhibitor — it blocks proteins called CDK4 and CDK6 that control how fast cells divide, which can slow or stop the growth of some breast cancers.
It is used for hormone-receptor-positive advanced or metastatic breast cancer, both HER2-negative and, as maintenance with trastuzumab, HER2-positive.
It is usually given as capsules or tablets taken by mouth, usually with a hormone therapy.
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The full explanation.
Slowing the cell's copy machine
Before a cell divides, it has to pass a checkpoint. Two proteins, CDK4 and CDK6, are what push it through. In many hormone-driven breast cancers that push is far too strong.
Palbociclib blocks CDK4 and CDK6. The cell stalls at the checkpoint instead of copying itself. It does not kill the cancer outright; it holds it still, which is why it is paired with a hormone treatment that starves it at the same time.
Ibrance is the brand name; palbociclib is the generic name.
It is never taken on its own
Every approved use of palbociclib is a combination. There is no approval for taking it alone.
The partner drug depends on the situation. It may be an aromatase inhibitor such as letrozole. It may be fulvestrant, given as an injection. It may be fulvestrant together with inavolisib. Or, in one setting, it is trastuzumab, sometimes with pertuzumab, plus hormone treatment.
If someone tells you to stop the partner drug, ask whether palbociclib should stop too. The pair is the treatment.
Which breast cancers it is approved for
The label covers advanced or spread breast cancer in adults, in these situations.
- Hormone-receptor-positive, HER2-negative disease, with an aromatase inhibitor as the first hormone-based treatment.
- The same disease, with fulvestrant, after hormone treatment has stopped working.
- Endocrine-resistant, PIK3CA-mutated, hormone-receptor-positive, HER2-negative disease, with inavolisib and fulvestrant, where the cancer returned during or after adjuvant hormone therapy.
- Hormone-receptor-positive, HER2-positive disease, with trastuzumab, with or without pertuzumab, and hormone therapy, as maintenance after the first phase of treatment.
Women before menopause also need treatment to switch off the ovaries alongside it.
Three weeks on, one week off
The rhythm is 21 days of capsules or tablets, then 7 days with none, making a 28-day cycle. Take it at about the same time each day.
The week off is deliberate. It gives the bone marrow time to recover. Skipping it is not a way to work harder at treatment.
If you vomit a dose or forget one, do not take an extra. Go back to the normal time the next day.
Capsules with food, tablets either way
This trips people up when a pharmacy switches the form.
Ibrance capsules must be taken with food. Ibrance tablets can be taken with or without food. Swallow either form whole. Do not chew, crush or open them, and do not use a capsule that is cracked or broken.
Avoid grapefruit and grapefruit juice with either form.
Low white cells are expected
Neutropenia — a drop in the white cells that fight bacteria — was the most common side effect in every major trial, seen in roughly 8 of every 10 people. That sounds alarming, and mostly it is manageable, because it is watched for and the dose is adjusted.
Blood is checked before you start, at the beginning of each of the first two cycles, on day 15 of those first two cycles, and then before each cycle after that.
A fever while your white cells are low needs attention the same hour, not at the next visit. CDC tells people having cancer treatment to call their doctor immediately for a temperature of 100.4 °F (38 °C) or higher. If you are sent to an emergency room, tell the staff you are on cancer treatment. Chills or shivering, a sore throat, burning when passing urine, or any other sign of infection with a fever belong in the same category. Do not wait for the next blood test.
Breathing changes to report
Inflammation of the lung tissue has happened with palbociclib and with other drugs in this class. It is uncommon, but there have been deaths.
Get emergency care for breathlessness that comes on suddenly, leaves you struggling to speak a full sentence, or comes with chest pain. Report a slower change — a new dry cough, mild breathlessness on stairs, or chest tightness — to your team the same day. Treatment is paused while it is looked into.
Tiredness, nausea, mouth soreness and thinning hair are the other frequent effects. Mouth care from day one — a soft brush, bland rinses, no alcohol mouthwash — prevents more trouble than treating it later.
Sources
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e0e6412f-50b4-4fd4-9364-62818d121a07
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fecbdd7d-b729-41b5-9872-231b8fe104ce
- https://www.cancer.gov/about-cancer/treatment/drugs/palbociclib
- https://www.cdc.gov/cancer-preventing-infections/patients/fever.html
Words to know
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Common questions
What is Ibrance?
Ibrance (Palbociclib) is a targeted therapy called a CDK4/6 inhibitor. It blocks proteins called CDK4 and CDK6 that control how fast cells divide, which can slow or stop the growth of some breast cancers. It is used for hormone-receptor-positive advanced or metastatic breast cancer that is HER2-negative, and as maintenance with trastuzumab where the cancer is HER2-positive.
How is Ibrance given?
It is usually given as capsules or tablets taken by mouth, usually with a hormone therapy. It is taken by mouth on a schedule (often 3 weeks on, 1 week off) together with a hormone-blocking medicine. Your team checks blood counts regularly. The exact schedule is set by your care team.
What are the common side effects of Ibrance?
Commonly reported side effects include low blood counts, tiredness, nausea, mouth sores, and hair thinning. Not everyone gets them, and many can be managed. Tell your care team about anything new or worsening.
Does Ibrance cure cancer?
That depends on the person, the cancer type, and its stage. For some people a medicine like this can control cancer for a long time or be part of a curative plan; for others the goal is to slow the cancer or ease symptoms. Your care team can explain the goal in your situation.
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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