Ibrance (chemical name: palbociclib) is a CDK4/6 inhibitor. Ibrance works against advanced-stage or metastatic, hormone-receptor-positive, HER2-negative breast cancer by stopping cancer cells from dividing and growing.

Ibrance (chemical name: palbociclib) is used in combination with a type of hormonal therapy called an aromatase inhibitor to treat advanced-stage or metastatic, hormone-receptor-positive, HER2-negative breast cancer that hasn’t been treated with hormonal therapy before in postmenopausal women or men. Arimidex (chemical name: anastrozole), Aromasin (chemical name: exemestane), and Femara (chemical name: letrozole) are aromatase inhibitors.

Ibrance also is approved to be used in combination with the hormonal therapy Faslodex (chemical name: fulvestrant) to treat advanced-stage or metastatic, hormone-receptor-positive, HER2-negative breast cancer that has grown after being treated with hormonal therapy in women or men. Premenopausal and perimenopausal women who take Ibrance in combination with Faslodex also should be treated with a medicine to suppress ovarian function.

Ibrance is a pill taken by mouth.


How Ibrance works

Cancer cells grow in uncontrolled fashion. Like Kisqali (chemical name: ribociclib) and Verzenio (chemical name: abemaciclib), Ibrance is a cyclin-dependent kinase (CDK) 4/6 inhibitor. A kinase is a type of protein in the body that helps control cell division. CDK4/6 inhibitors work by interfering with the kinase and stopping cancer cells from dividing and growing.


Is Ibrance right for you?

Ibrance can be prescribed with an aromatase inhibitor for postmenopausal women or men diagnosed with advanced-stage or metastatic, hormone-receptor-positive, HER2-negative breast cancer that hasn’t been treated with hormonal therapy yet.

Ibrance also can be used in combination with Faslodex in women or men to treat advanced-stage or metastatic, hormone-receptor-positive, HER2-negative breast cancer that has grown after being treated with hormonal therapy.

Advanced-stage breast cancer is cancer that has come back (recurred) or spread beyond the breast to the chest wall below the breast. Metastatic breast cancer is advanced-stage cancer that has spread to parts of the body away from the breast, such as the bones or liver.

Femara, Aromasin, and Arimidex are all aromatase inhibitors, a type of hormonal therapy. Aromatase inhibitors stop the production of the hormone estrogen. Aromatase inhibitors work by blocking the enzyme aromatase, which turns androgen hormones into small amounts of estrogen in the body. This means that less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells. All of the aromatase inhibitors are pills taken by mouth.

Faslodex is an estrogen receptor downregulator (ERD), another type of hormonal therapy. Faslodex blocks the effect of estrogen on breast tissue by sitting in the estrogen receptor in breast cells. Faslodex is a liquid given as an injection into a muscle.

To find out if a cancer is estrogen-receptor-positive, most testing labs use a special staining process that makes the hormone receptors show up in a tissue sample. The test is called an immunohistochemical staining assay, or ImmunoHistoChemistry (IHC). Not all labs use the same method for analyzing the results of the test, and they do not have to report the results in exactly the same way. So you may see any of the following on your pathology report:

  • A percentage that tells you how many cells out of 100 stain positive for hormone receptors. You will see a number between 0% (none have receptors) and 100% (all have receptors).

  • An Allred score between 0 and 8. This scoring system is named for the doctor who developed it. The system looks at what percentage of cells test positive for hormone receptors, along with how well the receptors show up after staining (this is called “intensity”). This information is then combined to score the sample on a scale from 0 to 8. The higher the score, the more receptors were found and the easier they were to see in the sample.

  • The word “positive” or “negative.” Learn more about how to read hormone receptor test results.

Learn more about how to read hormone receptor test results.


What to expect when taking Ibrance

The recommended starting dose of Ibrance is 125 mg. When taking Ibrance with an aromatase inhibitor, you take the pills in a 28-day cycle:

  • for 21 days, you take the Ibrance and aromatase inhibitor pills at the same time each day, with food

  • then for 7 days, you take the aromatase inhibitor only

You keep taking Ibrance with the aromatase inhibitor as long as you are getting benefits from the medicines and aren’t having troubling side effects.

When taking Ibrance with Faslodex, it’s also taken on a 28-day cycle:

  • you take Ibrance for 21 days at the same time each day, with food, then you stop taking the Ibrance pills for 7 days

  • you receive an injection of Faslodex every 2 weeks for the first three injections and then one injection every 4 weeks

There are certain medicines, supplements, and foods you should not take or eat if you are taking Ibrance:

  • You should not take a type of medicine called a CYP3A inhibitor because it increases the effects of Ibrance. This class of medicines includes antifungal medicines such as Onmel (chemical name: itraconazole) and Biaxin (chemical name: clarithromycin), as well as antiretroviral drugs used to treat HIV such as Kaletra (chemical name: lopinavir and ritonavir).

  • You should not take a type of medicine called a CYP3A inducer because it decreases the effects of Ibrance. This class of medicines includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy.

  • You should not take St. John’s wort, an herb that is sometimes used to control depression and anxiety, because it can decrease the effects of Ibrance.

  • You should not eat grapefruit or pomegranate or drink grapefruit juice or pomegranate juice because they can increase the effects of Ibrance.

It’s important to know that women who are pregnant or are planning to get pregnant should not take Ibrance. Doctors don’t know if Ibrance will harm your unborn baby. It’s important that you don’t get pregnant while you’re taking Ibrance; you must use effective birth control while you’re taking it and for at least 2 weeks after your last dose.

Men with female partners who can become pregnant should use birth control while they’re taking Ibrance for at least 3 months after the last dose.

Also, women who are breastfeeding or plan to breastfeed shouldn’t take Ibrance. Together, you and your doctor will decide if you should take Ibrance or breastfeed.

Visit Treatment for Breast Cancer During Pregnancy for more information.


Paying for Ibrance

If your doctor prescribes Ibrance and you have any problems getting it covered by insurance, or you don’t have insurance, the Pfizer RxPathways Program may be able to help. To talk to a Pfizer RxPathways patient care coordinator, call 1-877-744-5675 or visit Pfizer RxPathways.

Pfizer also offers the Pfizer Oncology Together Co-Pay Savings Card for eligible people who have health insurance. The card offers eligible people out-of-pocket costs savings for Ibrance. For more information and to see if you are eligible, visit the Pfizer Oncology Together Co-Pay Savings Program.


Ibrance side effects

The most common side effects of Ibrance are:

Less commonly, Ibrance may cause serious side effects, including:

Severe neutropenia (very low white blood cell count): Low white blood cell counts are a common side effect of Ibrance. Still, some people’s white blood cell counts may drop so low that they have to decrease the dose or of Ibrance or stop treatment. Your doctor will check your white blood cell count before and during treatment with Ibrance.

Rare but severe lung inflammation: In some people, Ibrance may lead to severe pneumonia or interstitial lung disease. Interstitial lung disease describes a large group of conditions that cause scarring of the lungs. The scarring makes the lungs stiff, which makes it difficult to breathe. Tell your doctor right away if you have difficulty breathing or discomfort when you breathe or have shortness of breath when you’re resting or doing an activity that requires little exertion.

Infections: Ibrance may make some women more likely to develop infections such as pneumonia or other upper respiratory infections. Tell your doctor right away if you have a temperature higher than 100.5 degrees F, chills, or don’t feel well.

Blood clots: Ibrance may cause serious or life-threatening blood clots in your arteries or lungs. Tell your doctor right away if you have shortness of breath, rapid heart rate, rapid breathing, or a sudden sharp chest pain.

Because Ibrance is given with an aromatase inhibitor or Faslodex (chemical name: fulvestrant), you also may have side effects from those medicines. Common side effects of aromatase inhibitors are bone thinning and bone and joint pain. Common side effects of Faslodex are hot flashes and nausea.


Ibrance (palbociclib) prescribing information. Pfizer. New York, NY. 2018. Available at https://labeling.pfizer.com/ShowLabeling.aspx?id=2191 

— Last updated on March 31, 2022, 7:11 PM

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