CDK4/6 Inhibitors for Metastatic Breast Cancer
CDK4 and CDK6 are enzymes important in cell division. CDK4/6 inhibitors are drugs designed to interrupt the growth of cancer cells.
CDK4/6 inhibitors are used in combination with hormone therapy to treat some hormone receptor-positive breast cancers.
The CDK4/6 inhibitors FDA-approved for metastatic breast cancer treatment are:
Drug name |
Brand name |
How is it given? |
Abemaciclib |
Verzenio |
Pill |
Palbociclib |
Ibrance |
Pill |
Ribociclib |
Kisqali |
Pill |
Although the CDK4/6 inhibitors abemaciclib, palbociclib and ribociclib haven’t been compared directly to one another, studies show similar results with each drug in treating metastatic breast cancer [6-14].
CDK4/6 inhibitors and metastatic breast cancer treatment
CDK4/6 inhibitors are used in combination with hormone therapy (an aromatase inhibitor or fulvestrant).
A CDK4/6 inhibitor in combination with hormone therapy can be used to treat some metastatic breast cancers that are:
Compared to treatment with hormone therapy alone, the combination of hormone therapy and a CDK4/6 inhibitor can give people more time before the cancer worsens and increase overall survival [6-16].
The CDK4/6 inhibitor abemaciclib may also be used alone to treat hormone receptor-positive, HER2-negative cancers that have progressed on past hormone therapy and chemotherapy [4].
| For a summary of research studies on CDK4/6 inhibitors and metastatic breast cancer treatment, visit the Breast Cancer Research Studies section. |
Learn more about hormone therapy in the treatment of metastatic breast cancer.
Learn more about treatment for metastatic breast cancer.
Learn more about emerging areas in treatment for metastatic breast cancer.
Learn about the CDK4/6 inhibitor abemaciclib in the treatment of early breast cancer.
How are CDK4/6 inhibitors given?
The CDK4/6 inhibitors abemaciclib, palbociclib and ribociclib are pills.
Side effects of CDK4/6 inhibitors
The table below lists some possible side effects of CDK4/6 inhibitors.
CDK4/6 Inhibitor |
Side Effects |
Abemaciclib |
Possible side effects include diarrhea, low white blood cell counts, anemia (low red blood cell counts), blood clots, nausea, abdominal pain, fatigue and vomiting. In some cases, it can cause liver problems. Your liver function will be checked before treatment begins and throughout your treatment. In rare cases, it can cause lung inflammation, which can lead to death. Tell your health care provider right away if you have shortness of breath or other breathing problems while taking this drug. |
Palbociclib |
Possible side effects include low white blood cell counts, anemia (low red blood cell counts), fatigue, nausea, mouth sores, hair thinning, diarrhea and in rare cases, blood clots. In rare cases, it can cause lung inflammation, which can lead to death. Tell your health care provider right away if you have shortness of breath or other breathing problems while taking this drug. |
Ribociclib |
Possible side effects include low white blood cell counts, nausea, fatigue, diarrhea, hair loss, vomiting, constipation, headache and back pain. In some cases, it can cause liver problems. Your liver function will be checked before treatment begins and throughout your treatment. In rare cases, it can cause changes on an EKG (electrocardiogram). An EKG gives information on the electrical activity of the heart. You will get an EKG before treatment begins and throughout your treatment to check for any changes. In rare cases, it can cause lung inflammation, which can lead to death. Tell your health care provider right away if you have shortness of breath or other breathing problems while taking this drug. |
Adapted from select sources [6-19]. | |
Grapefruit and grapefruit juice should be avoided while taking a CDK4/6 inhibitor, as they may increase blood levels of the drug [17-19].
Before you begin taking a CDK4/6 inhibitor, talk with your health care provider about possible side effects and how to manage them.
Monitoring metastatic breast cancer
You’ll be monitored (checked) regularly with scans to see if the cancer is responding to treatment. If it’s no longer working, or if the side effects are not manageable, your health care provider will change your treatment or discuss other options.
Learn more about how metastatic breast cancer is monitored.
Clinical trials
Clinical trials offer the chance to try new treatments and possibly benefit from them.
Many clinical trials are available. Some are for the first treatment a person might get for their metastatic breast cancer, and others are for treatments later in the disease course. Consider joining a clinical trial when you’re newly diagnosed, when your oncologist is considering changing treatments or when there are limited treatment options.
Susan G. Komen® Breast Care Helpline |
If you or a loved one needs information or resources about clinical trials, call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877- 465- 6636) or email clinicaltrialinfo@komen.org. Se habla español. |
Metastatic Trial Search |
The Metastatic Trial Search is a web-based clinical trial matching tool that can help you find clinical trials that fit your needs. |
Learn more about clinical trials for people with metastatic breast cancer.
Prescription drug assistance
The cost of drug therapies for metastatic breast cancer can quickly become a financial burden for you and your family.
Medicare and many insurance companies offer prescription drug plans. One may already be included in your policy, or you may be able to buy an extra plan for prescriptions.
You may also qualify for programs that help with drug costs or offer low-cost or free prescriptions.
Many cancer centers have patient financial counselors who can discuss insurance and cost coverage with you.
Learn more about insurance plans and prescription drug assistance programs.
Learn more about other financial assistance programs.
Komen Financial Assistance Program |
Susan G. Komen® created the Komen Financial Assistance Program to help those struggling with the costs of breast cancer treatment by providing financial assistance to eligible individuals. Funding is available for eligible individuals undergoing breast cancer treatment at any stage or living with metastatic breast cancer (stage 4). To learn more about this program and other helpful resources, call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636) or email helpline@komen.org. Se habla español. |
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Susan G. Komen®‘s position on fairness in oral cancer drug coverage |
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Insurance coverage of oral cancer drugs Cancer medications given by vein (through an IV) or injection (under the skin or into a muscle) are usually covered under a health insurance plan’s medical benefit. However, cancer medications that are pills (oral cancer drugs) are usually covered under a health insurance plan’s prescription drug benefit. As a result, people often find themselves facing high out-of-pocket costs when filling prescriptions for oral cancer drugs. Sometimes these costs can be thousands of dollars a month. The impact of high cost-sharing High prescription drug costs and the resulting out-of-pocket burden on patients are a barrier to care. They can prevent people from getting the medications prescribed by their health care providers. No one should be forced to get less appropriate treatment because an insurer gives more coverage for IV and injectable drugs than pills. Efforts to increase fairness in drug coverage Komen supports state and federal efforts to require insurers to provide the same or better coverage for oral cancer drugs as they do for IV and injectable cancer drugs. This would help make sure patients have access to affordable, appropriate treatment. Become a Komen Advocacy Insider Sign up to be a Komen Advocacy Insider and get informed when action is needed on drug coverage issues at the state or national level. |
SUSAN G. KOMEN® METASTATIC BREAST CANCER SUPPORT RESOURCES |
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Updated 06/25/23
